Frequently Asked Questions (FAQ) for PostgreSQL
- Last updated: Fri Jun 2 11:32:13 EDT 2000
+ Last updated: Tue Oct 17 00:21:20 EDT 2000
- The most recent version of this document can be viewed at the
- postgreSQL Web site, http://www.PostgreSQL.org.
+ The most recent version of this document can be viewed at
+ http://www.PostgreSQL.org/docs/faq-english.html.
- Linux-specific questions are answered in
- http://www.PostgreSQL.org/docs/faq-linux.html.
-
- HPUX-specific questions are answered in
- http://www.PostgreSQL.org/docs/faq-hpux.html.
-
- Solaris-specific questions are answered in
- http://www.postgresql.org/docs/faq-solaris.html.
-
- Irix-specific questions are answered in
- http://www.PostgreSQL.org/docs/faq-irix.html.
+ Platform-specific questions are answered at
+ http://www.PostgreSQL.org/docs/.
_________________________________________________________________
General Questions
1.3) What Unix platforms does PostgreSQL run on?
1.4) What non-unix ports are available?
1.5) Where can I get PostgreSQL?
- 1.6) Where can I get support for PostgreSQL?
- 1.7) What is the latest release of PostgreSQL?
- 1.8) What documentation is available for PostgreSQL?
+ 1.6) Where can I get support?
+ 1.7) What is the latest release?
+ 1.8) What documentation is available?
1.9) How do I find out about known bugs or missing features?
1.10) How can I learn SQL?
1.11) Is PostgreSQL Y2K compliant?
/usr/local/pgsql?
3.3) When I start the postmaster, I get a Bad System Call or core
dumped message. Why?
- 3.4) When I try to start the postmaster, I get IpcMemoryCreate
- errors3. Why?
+ 3.4) When I try to start the postmaster, I get IpcMemoryCreate errors.
+ Why?
3.5) When I try to start the postmaster, I get IpcSemaphoreCreate
errors. Why?
3.6) How do I prevent other hosts from accessing my PostgreSQL
3.8) Why can't I access the database as the root user?
3.9) All my servers crash under concurrent table access. Why?
3.10) How do I tune the database engine for better performance?
- 3.11) What debugging features are available in PostgreSQL?
- 3.12) I get 'Sorry, too many clients' when trying to connect. Why?
- 3.13) What are the pg_psort.XXX files in my database directory?
+ 3.11) What debugging features are available?
+ 3.12) I get "Sorry, too many clients" when trying to connect. Why?
+ 3.13) What are the pg_sorttempNNN.NN files in my database directory?
Operational Questions
- 4.1) The system seems to be confused about commas, decimal points, and
- date formats.
+ 4.1) Why is the system confused about commas, decimal points, and date
+ formats.
4.2) What is the exact difference between binary cursors and normal
cursors?
- 4.3) How do I select only the first few rows of a query?
- 4.4) How do I get a list of tables, or other things I can see in psql?
+ 4.3) How do I SELECT only the first few rows of a query?
+ 4.4) How do I get a list of tables or other things I can see in psql?
4.5) How do you remove a column from a table?
4.6) What is the maximum size for a row, table, database?
4.7) How much database disk space is required to store data from a
- typical flat file?
+ typical text file?
4.8) How do I find out what indices or operations are defined in the
database?
4.9) My queries are slow or don't make use of the indexes. Why?
4.11) What is an R-tree index?
4.12) What is Genetic Query Optimization?
4.13) How do I do regular expression searches and case-insensitive
- regexp searching?
+ regular expression searches?
4.14) In a query, how do I detect if a field is NULL?
4.15) What is the difference between the various character types?
4.16.1) How do I create a serial/auto-incrementing field?
- 4.16.2) How do I get the value of a serial insert?
+ 4.16.2) How do I get the value of a SERIAL insert?
4.16.3) Don't currval() and nextval() lead to a race condition with
- other concurrent backend processes?
- 4.17) What is an oid? What is a tid?
+ other users?
+ 4.17) What is an OID? What is a TID?
4.18) What is the meaning of some of the terms used in PostgreSQL?
4.19) Why do I get the error "FATAL: palloc failure: memory
exhausted?"
5.1) I wrote a user-defined function. When I run it in psql, why does
it dump core?
- 5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0
- not in alloc set! mean?
- 5.3) How can I contribute some nifty new types and functions for
+ 5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0
+ not in alloc set!" mean?
+ 5.3) How can I contribute some nifty new types and functions to
PostgreSQL?
5.4) How do I write a C function to return a tuple?
- 5.5) I have changed a source file. Why does the recompile does not see
- the change?
+ 5.5) I have changed a source file. Why does the recompile not see the
+ change?
_________________________________________________________________
General Questions
replaces the PostQuel query language with an extended subset of SQL.
PostgreSQL is free and the complete source is available.
- PostgreSQL development is being performed by a team of Internet
- developers who all subscribe to the PostgreSQL development mailing
- list. The current coordinator is Marc G. Fournier
- responsible for all current and future development of PostgreSQL.
+ PostgreSQL development is performed by a team of Internet developers
+ who all subscribe to the PostgreSQL development mailing list. The
+ below on how to join). This team is now responsible for all
+ development of PostgreSQL.
The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
- others have contributed to the porting, testing, debugging and
+ others have contributed to the porting, testing, debugging, and
enhancement of the code. The original Postgres code, from which
PostgreSQL is derived, was the effort of many graduate students,
undergraduate students, and staff programmers working under the
1.2) What's the copyright on PostgreSQL?
- PostgreSQL is subject to the following COPYRIGHT.
+ PostgreSQL is subject to the following COPYRIGHT:
PostgreSQL Data Base Management System
A file win31.mak is included in the distribution for making a Win32
libpq library and psql.
- The database server is now working on Windows NT using the Cygnus
- Unix/NT porting library. See pgsql/doc/README.NT in the distribution.
-
- There is also a web page at
- http://www.freebsd.org/~kevlo/postgres/portNT.html. There is another
- port using U/Win at http://surya.wipro.com/uwin/ported.html.
+ The database server is now working on Windows NT using Cygwin, the
+ Cygnus Unix/NT porting library. See pgsql/doc/FAQ_NT in the
+ distribution. It does not work on MS Windows 9X because Cygwin does
+ not support the features we need on those platforms.
1.5) Where can I get PostgreSQL?
The primary anonymous ftp site for PostgreSQL is
- ftp://ftp.postgreSQL.org/pub
+ ftp://ftp.PostgreSQL.org/pub. For mirror sites, see our main Web site.
- For mirror sites, see our main web site.
-
- 1.6) Where can I get support for PostgreSQL?
+ 1.6) Where can I get support?
- There is no official support for PostgreSQL from the University of
- California, Berkeley. It is maintained through volunteer effort.
+ There is no support for PostgreSQL from the University of California,
+ Berkeley. It is maintained through volunteer effort.
- The main mailing list is: pgsql-general@postgreSQL.org. It is
+ The main mailing list is: pgsql-general@PostgreSQL.org. It is
available for discussion of matters pertaining to PostgreSQL. To
- subscribe, send a mail with the lines in the body (not the subject
- line)
+ subscribe, send mail with the following lines in the body (not the
+ subject line)
subscribe
end
- to pgsql-general-request@postgreSQL.org.
+ to pgsql-general-request@PostgreSQL.org.
There is also a digest list available. To subscribe to this list, send
- email to: pgsql-general-digest-request@postgreSQL.org with a BODY of:
+ email to: pgsql-general-digest-request@PostgreSQL.org with a body of:
subscribe
end
has received around 30k of messages.
The bugs mailing list is available. To subscribe to this list, send
subscribe
end
There is also a developers discussion mailing list available. To
- with a BODY of:
+ subscribe to this list, send email to
subscribe
end
Additional mailing lists and information about PostgreSQL can be found
via the PostgreSQL WWW home page at:
- http://postgreSQL.org
+ http://www.PostgreSQL.org
There is also an IRC channel on EFNet, channel #PostgreSQL. I use the
- unix command irc -c '#PostgreSQL' "$USER" irc.phoenix.net
+ unix command irc -c '#PostgreSQL' "$USER" irc.phoenix.net.
Commercial support for PostgreSQL is available at
- http://www.pgsql.com/
+ http://www.pgsql.com/.
- 1.7) What is the latest release of PostgreSQL?
+ 1.7) What is the latest release?
The latest release of PostgreSQL is version 7.0.2.
We plan to have major releases every four months.
- 1.8) What documentation is available for PostgreSQL?
+ 1.8) What documentation is available?
Several manuals, manual pages, and some small test examples are
included in the distribution. See the /doc directory. You can also
- browse the manual on-line at http://www.postgresql.org/docs/postgres.
- in the distribution.
+ browse the manual online at http://www.PostgreSQL.org/docs/postgres.
- There is a PostgreSQL book availiable at
- http://www.postgresql.org/docs/awbook.html
+ There is a PostgreSQL book available at
+ http://www.PostgreSQL.org/docs/awbook.html.
psql has some nice \d commands to show information about types,
operators, functions, aggregates, etc.
- The web site contains even more documentation.
+ Our Web site contains even more documentation.
1.9) How do I find out about known bugs or missing features?
- PostgreSQL supports an extended subset of SQL-92. See our TODO for a
- list of known bugs, missing features, and future plans.
+ PostgreSQL supports an extended subset of SQL-92. See our TODO list
+ for known bugs, missing features, and future plans.
1.10) How can I learn SQL?
- The PostgreSQL book at http://www.postgresql.org/docs/awbook.html
+ The PostgreSQL book at http://www.PostgreSQL.org/docs/awbook.html
teaches SQL. There is a nice tutorial at
http://w3.one.net/~jhoffman/sqltut.htm and at
http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM.
Another one is "Teach Yourself SQL in 21 Days, Second Edition" at
http://members.tripod.com/er4ebus/sql/index.htm
- Many of our users like The Practical SQL Handbook, Bowman et al.,
- Addison Wesley. Others like The Complete Reference SQL, Groff et al.,
- McGraw-Hill.
+ Many of our users like The Practical SQL Handbook, Bowman, Judith S.,
+ et al., Addison-Wesley. Others like The Complete Reference SQL, Groff
+ et al., McGraw-Hill.
1.11) Is PostgreSQL Y2K compliant?
1.12) How do I join the development team?
- First, download the latest sources and read the PostgreSQL Developers
- documentation on our web site, or in the distribution. Second,
+ First, download the latest source and read the PostgreSQL Developers
+ documentation on our Web site, or in the distribution. Second,
subscribe to the pgsql-hackers and pgsql-patches mailing lists. Third,
submit high-quality patches to pgsql-patches.
- There are about a dozen people who have COMMIT privileges to the
- PostgreSQL CVS archive. All of them have submitted so many
- high-quality patches that it was a pain for the existing committers to
- keep up, and we had confidence that patches they committed were likely
- to be of high quality.
+ There are about a dozen people who have commit privileges to the
+ PostgreSQL CVS archive. They each have submitted so many high-quality
+ patches that it was impossible for the existing committers to keep up,
+ and we had confidence that patches they committed were of high
+ quality.
1.13) How do I submit a bug report?
+ Fill out the "bug-template" file and send it to:
- Also check out our ftp site ftp://ftp.postgreSQL.org/pub to see if
+ Also check out our ftp site ftp://ftp.PostgreSQL.org/pub to see if
there is a more recent PostgreSQL version or patches.
1.14) How does PostgreSQL compare to other DBMS's?
some features they don't have, like user-defined types,
inheritance, rules, and multi-version concurrency control to
reduce lock contention. We don't have outer joins, but are
- working on them for our next release.
+ working on them.
Performance
PostgreSQL runs in two modes. Normal fsync mode flushes every
though in this mode, an OS crash could cause data corruption.
We are working to provide an intermediate mode that suffers
less performance overhead than full fsync mode, and will allow
- data integrity within 30 seconds of an OS crash. The mode is
- select-able by the database administrator.
+ data integrity within 30 seconds of an OS crash.
In comparison to MySQL or leaner database systems, we are
slower on inserts/updates because we have transaction overhead.
Of course, MySQL doesn't have any of the features mentioned in
the Features section above. We are built for flexibility and
features, though we continue to improve performance through
- profiling and source code analysis. There is an interesting web
+ profiling and source code analysis. There is an interesting Web
page comparing PostgreSQL to MySQL at
http://openacs.org/why-not-mysql.html
We handle each user connection by creating a Unix process.
There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.
PsqlODBC is included in the distribution. More information about it
- can be gotten from: ftp://ftp.postgresql.org/pub/odbc/index.html
+ can be gotten from ftp://ftp.PostgreSQL.org/pub/odbc/.
OpenLink ODBC can be gotten from http://www.openlinksw.com. It works
with their standard ODBC client software so you'll have PostgreSQL
There is also one at http://www.phone.net/home/mwm/hotlist/.
- For web integration, PHP is an excellent interface. It is at:
+ For Web integration, PHP is an excellent interface. It is at
http://www.php.net
- PHP is great for simple stuff, but for more complex cases, many use
- the perl interface and CGI.pm.
+ For complex cases, many use the Perl interface and CGI.pm.
- A WWW gateway based on WDB using perl can be downloaded from
+ A WWW gateway based on WDB using Perl can be downloaded from
http://www.eol.ists.ca/~dunlop/wdb-p95
2.3) Does PostgreSQL have a graphical user interface? A report generator?
We have a nice graphical user interface called pgaccess, which is
shipped as part of the distribution. Pgaccess also has a report
- generator. The web page is http://www.flex.ro/pgaccess
+ generator. The Web page is http://www.flex.ro/pgaccess
We also include ecpg, which is an embedded SQL query language
interface for C.
2.4) What languages are available to communicate with PostgreSQL?
We have:
- * C(libpq)
- * C++(libpq++)
- * Embedded C(ecpg)
- * Java(jdbc)
- * Perl(perl5)
- * ODBC(odbc)
- * Python(PyGreSQL)
- * TCL(libpgtcl)
- * C Easy API(libpgeasy)
- * Embedded HTML(PHP from http://www.php.net)
+ * C (libpq)
+ * C++ (libpq++)
+ * Embedded C (ecpg)
+ * Java (jdbc)
+ * Perl (perl5)
+ * ODBC (odbc)
+ * Python (PyGreSQL)
+ * TCL (libpgtcl)
+ * C Easy API (libpgeasy)
+ * Embedded HTML (PHP from http://www.php.net)
_________________________________________________________________
Administrative Questions
3.1) Why does initdb fail?
+ Try these:
* check that you don't have any of the previous version's binaries
in your path
* check to see that you have the proper paths set
* check that the postgres user owns the proper files
+ If you see an error message about oidvector, you definately have a
+ version mismatch.
+
3.2) How do I install PostgreSQL somewhere other than /usr/local/pgsql?
The simplest way is to specify the --prefix option when running
message. Why?
It could be a variety of problems, but first check to see that you
- have system V extensions installed in your kernel. PostgreSQL requires
+ have System V extensions installed in your kernel. PostgreSQL requires
kernel support for shared memory and semaphores.
3.4) When I try to start the postmaster, I get IpcMemoryCreate errors. Why?
- You either do not have shared memory configured properly in kernel or
- you need to enlarge the shared memory available in the kernel. The
- exact amount you need depends on your architecture and how many
- buffers and backend processes you configure postmaster to run with.
+ You either do not have shared memory configured properly in your
+ kernel or you need to enlarge the shared memory available in the
+ kernel. The exact amount you need depends on your architecture and how
+ many buffers and backend processes you configure for the postmaster.
For most systems, with default numbers of buffers and processes, you
need a minimum of ~1MB.
The default configuration allows only unix domain socket connections
from the local machine. To enable TCP/IP connections, make sure the
postmaster has been started with the -i option, and add an appropriate
- host entry to the file pgsql/data/pg_hba.conf. See the pg_hba.conf
- manual page.
+ host entry to the file pgsql/data/pg_hba.conf.
3.8) Why can't I access the database as the root user?
You should not create database users with user id 0 (root). They will
be unable to access the database. This is a security precaution
- because of the ability of any user to dynamically link object modules
+ because of the ability of users to dynamically link object modules
into the database engine.
3.9) All my servers crash under concurrent table access. Why?
indices are being used.
If you are doing a lot of INSERTs, consider doing them in a large
- batch using the COPY command. This is much faster than single
- individual INSERTS. Second, statements not in a BEGIN WORK/COMMIT
- transaction block are considered to be in their own transaction.
- Consider performing several statements in a single transaction block.
- This reduces the transaction overhead. Also consider dropping and
+ batch using the COPY command. This is much faster than individual
+ INSERTS. Second, statements not in a BEGIN WORK/COMMIT transaction
+ block are considered to be in their own transaction. Consider
+ performing several statements in a single transaction block. This
+ reduces the transaction overhead. Also consider dropping and
recreating indices when making large data changes.
- There are several tuning things that can be done. You can disable
- fsync() by starting the postmaster with a -o -F option. This will
- prevent fsync()'s from flushing to disk after every transaction.
+ There are several tuning options. You can disable fsync() by starting
+ the postmaster with a -o -F option. This will prevent fsync()'s from
+ flushing to disk after every transaction.
You can also use the postmaster -B option to increase the number of
shared memory buffers used by the backend processes. If you make this
- parameter too high, the postmaster may not start up because you've
+ parameter too high, the postmaster may not start because you've
exceeded your kernel's limit on shared memory space. Each buffer is 8K
and the default is 64 buffers.
of memory used by the backend process for temporary sorts. The -S
value is measured in kilobytes, and the default is 512 (ie, 512K).
- You can also use the CLUSTER command to group data in base tables to
- match an index. See the cluster(l) manual page for more details.
+ You can also use the CLUSTER command to group data in tables to match
+ an index. See the CLUSTER manual page for more details.
- 3.11) What debugging features are available in PostgreSQL?
+ 3.11) What debugging features are available?
PostgreSQL has several features that report status information that
can be valuable for debugging purposes.
You need to increase the postmaster's limit on how many concurrent
backend processes it can start.
- In Postgres 6.5 and up, the default limit is 32 processes. You can
+ In PostgreSQL 6.5 and up, the default limit is 32 processes. You can
increase it by restarting the postmaster with a suitable -N value.
- With the default configuration you can set -N as large as 1024; if you
+ With the default configuration you can set -N as large as 1024. If you
need more, increase MAXBACKENDS in include/config.h and rebuild. You
can set the default value of -N at configuration time, if you like,
using configure's --with-maxbackends switch.
should be more than that for best performance. For large numbers of
backend processes, you are also likely to find that you need to
increase various Unix kernel configuration parameters. Things to check
- include the maximum size of shared memory blocks, SHMMAX, the maximum
- number of semaphores, SEMMNS and SEMMNI, the maximum number of
- processes, NPROC, the maximum number of processes per user, MAXUPRC,
+ include the maximum size of shared memory blocks, SHMMAX; the maximum
+ number of semaphores, SEMMNS and SEMMNI; the maximum number of
+ processes, NPROC; the maximum number of processes per user, MAXUPRC;
and the maximum number of open files, NFILE and NINODE. The reason
- that Postgres has a limit on the number of allowed backend processes
- is so that you can ensure that your system won't run out of resources.
+ that PostgreSQL has a limit on the number of allowed backend processes
+ is so your system won't run out of resources.
- In Postgres versions prior to 6.5, the maximum number of backends was
- 64, and changing it required a rebuild after altering the MaxBackendId
- constant in include/storage/sinvaladt.h.
+ In PostgreSQL versions prior to 6.5, the maximum number of backends
+ was 64, and changing it required a rebuild after altering the
+ MaxBackendId constant in include/storage/sinvaladt.h.
- 3.13) What are the pg_tempNNN.NN files in my database directory?
+ 3.13) What are the pg_sorttempNNN.NN files in my database directory?
They are temporary files generated by the query executor. For example,
if a sort needs to be done to satisfy an ORDER BY, and the sort
- requires more space than the backend's -S parameter allows, then temp
- files are created to hold the extra data.
+ requires more space than the backend's -S parameter allows, then
+ temporary files are created to hold the extra data.
- The temp files should go away automatically, but might not if a
- backend crashes during a sort. If you have no transactions running at
+ The temporary files should be deleted automatically, but might not if
+ a backend crashes during a sort. If you have no backends running at
the time, it is safe to delete the pg_tempNNN.NN files.
_________________________________________________________________
Operational Questions
- 4.1) The system seems to be confused about commas, decimal points, and date
- formats.
+ 4.1) Why is system confused about commas, decimal points, and date formats.
- Check your locale configuration. PostgreSQL uses the locale settings
- of the user that ran the postmaster process. There are postgres and
- psql SET commands to control the date format. Set those accordingly
- for your operating environment.
+ Check your locale configuration. PostgreSQL uses the locale setting of
+ the user that ran the postmaster process. There are postgres and psql
+ SET commands to control the date format. Set those accordingly for
+ your operating environment.
4.2) What is the exact difference between binary cursors and normal
cursors?
only the first few records requested, or the entire query may have to
be evaluated until the desired rows have been generated.
- 4.4) How do I get a list of tables, or other information I see in psql?
+ 4.4) How do I get a list of tables or other things I can see in psql?
- You can read the source code for psql, file pgsql/src/bin/psql/psql.c.
- It contains SQL commands that generate the output for psql's backslash
- commands. You can also start psql with the -E option so that it will
- print out the queries it uses to execute the commands you give.
+ You can read the source code for psql in file
+ pgsql/src/bin/psql/psql.c. It contains SQL commands that generate the
+ output for psql's backslash commands. You can also start psql with the
+ -E option so it will print out the queries it uses to execute the
+ commands you give.
4.5) How do you remove a column from a table?
Maximum size for a table? unlimited on all operating systems
Maximum size for a row? 8k, configurable to 32k
Maximum number of rows in a table? unlimited
-Maximum number of columns table? unlimited
+Maximum number of columns in a table? unlimited
Maximum number of indexes on a table? unlimited
Of course, these are not actually unlimited, but limited to available
BLCKSZ. To use attributes larger than 8K, you can also use the large
object interface.
- Row length limit will be removed in 7.1.
+ The row length limit will be removed in 7.1.
- 4.7)How much database disk space is required to store data from a typical
- flat file?
+ 4.7) How much database disk space is required to store data from a typical
+ text file?
- A Postgres database can require about six and a half times the disk
- space required to store the data in a flat file.
+ A PostgreSQL database may need six-and-a-half times the disk space
+ required to store the data in a flat file.
Consider a file of 300,000 lines with two integers on each line. The
flat file is 2.4MB. The size of the PostgreSQL database file
1755 database pages * 8192 bytes per page = 14,376,960 bytes (14MB)
- Indexes do not contain as much overhead, but do contain the data that
+ Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also.
4.8) How do I find out what indices or operations are defined in the
4.9) My queries are slow or don't make use of the indexes. Why?
- PostgreSQL does not automatically maintain statistics. One has to make
- an explicit VACUUM call to update the statistics. After statistics are
- updated, the optimizer knows how many rows in the table, and can
- better decide if it should use indices. Note that the optimizer does
- not use indices in cases when the table is small because a sequential
- scan would be faster.
+ PostgreSQL does not automatically maintain statistics. VACUUM must be
+ run to update the statistics. After statistics are updated, the
+ optimizer knows how many rows in the table, and can better decide if
+ it should use indices. Note that the optimizer does not use indices in
+ cases when the table is small because a sequential scan would be
+ faster.
For column-specific optimization statistics, use VACUUM ANALYZE.
- VACUUM ANALYZE is important for complex multi-join queries, so the
+ VACUUM ANALYZE is important for complex multijoin queries, so the
optimizer can estimate the number of rows returned from each table,
and choose the proper join order. The backend does not keep track of
column statistics on its own, so VACUUM ANALYZE must be run to collect
4.11) What is an R-tree index?
- An r-tree index is used for indexing spatial data. A hash index can't
+ An R-tree index is used for indexing spatial data. A hash index can't
handle range searches. A B-tree index only handles range searches in a
single dimension. R-tree's can handle multi-dimensional data. For
example, if an R-tree index can be built on an attribute of type
- point, the system can more efficient answer queries like select all
- points within a bounding rectangle.
+ point, the system can more efficiently answer queries such as "select
+ all points within a bounding rectangle."
- The canonical paper that describes the original R-Tree design is:
+ The canonical paper that describes the original R-tree design is:
- Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial
+ Guttman, A. "R-trees: A Dynamic Index Structure for Spatial
Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data,
45-57.
You can also find this paper in Stonebraker's "Readings in Database
- Systems"
+ Systems".
- Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
+ Built-in R-trees can handle polygons and boxes. In theory, R-trees can
be extended to handle higher number of dimensions. In practice,
- extending R-trees require a bit of work and we don't currently have
+ extending R-trees requires a bit of work and we don't currently have
any documentation on how to do it.
4.12) What is Genetic Query Optimization?
- The GEQO module in PostgreSQL is intended to solve the query
- optimization problem of joining many tables by means of a Genetic
- Algorithm (GA). It allows the handling of large join queries through
- non-exhaustive search.
-
- For further information see the documentation.
+ The GEQO module speeds query optimization when joining many tables by
+ means of a Genetic Algorithm (GA). It allows the handling of large
+ join queries through nonexhaustive search.
- 4.13) How do I do regular expression searches and case-insensitive regexp
- searching?
+ 4.13) How do I do regular expression searches and case-insensitive regular
+ expression searches?
- The ~ operator does regular-expression matching, and ~* does
- case-insensitive regular-expression matching. There is no
+ The ~ operator does regular expression matching, and ~* does
+ case-insensitive regular expression matching. There is no
case-insensitive variant of the LIKE operator, but you can get the
effect of case-insensitive LIKE with this:
WHERE lower(textfield) LIKE lower(pattern)
You will see the internal name when examining system catalogs and in
some error messages.
- The last four types above are "varlena" types (i.e. the first four
+ The last four types above are "varlena" types (i.e., the first four
bytes are the length, followed by the data). char(#) allocates the
maximum number of bytes no matter how much data is stored in the
field. text, varchar(#), and bytea all have variable length on the
4.16.1) How do I create a serial/auto-incrementing field?
- PostgreSQL supports SERIAL data type. It auto-creates a sequence and
- index on the column. For example, this...
+ PostgreSQL supports a SERIAL data type. It auto-creates a sequence and
+ index on the column. For example, this:
CREATE TABLE person (
id SERIAL,
name TEXT
);
- ...is automatically translated into this...
+ is automatically translated into this:
CREATE SEQUENCE person_id_seq;
CREATE TABLE person (
id INT4 NOT NULL DEFAULT nextval('person_id_seq'),
CREATE UNIQUE INDEX person_id_key ON person ( id );
See the create_sequence manual page for more information about
- sequences. You can also use each row's oid field as a unique value.
+ sequences. You can also use each row's OID field as a unique value.
However, if you need to dump and reload the database, you need to use
- pg_dump's -o option or COPY WITH OIDS option to preserve the oids.
+ pg_dump's -o option or COPY WITH OIDS option to preserve the OIDs.
- For more details, see Bruce Momjian's chapter on Numbering Rows.
+ Numbering Rows.
- 4.16.2) How do I get the back the generated SERIAL value after an insert?
+ 4.16.2) How do I get the value of a SERIAL insert?
- Probably the simplest approach is to to retrieve the next SERIAL value
- from the sequence object with the nextval() function before inserting
- and then insert it explicitly. Using the example table in 4.16.1, that
- might look like this:
+ One approach is to to retrieve the next SERIAL value from the sequence
+ object with the nextval() function before inserting and then insert it
+ explicitly. Using the example table in 4.16.1, that might look like
+ this:
$newSerialID = nextval('person_id_seq');
INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
You would then also have the new value stored in $newSerialID for use
in other queries (e.g., as a foreign key to the person table). Note
- that the name of the automatically-created SEQUENCE object will be
+ that the name of the automatically created SEQUENCE object will be
named <table>_<serialcolumn>_seq, where table and serialcolumn are the
names of your table and your SERIAL column, respectively.
- Similarly, you could retrieve the just-assigned SERIAL value with the
+ Alternatively, you could retrieve the assigned SERIAL value with the
currval() function after it was inserted by default, e.g.,
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
- Finally, you could use the oid returned from the INSERT statement to
- lookup the default value, though this is probably the least portable
- approach. In perl, using DBI with Edmund Mergl's DBD::Pg module, the
+ Finally, you could use the OID returned from the INSERT statement to
+ look up the default value, though this is probably the least portable
+ approach. In Perl, using DBI with Edmund Mergl's DBD::Pg module, the
oid value is made available via $sth->{pg_oid_status} after
$sth->execute().
4.16.3) Don't currval() and nextval() lead to a race condition with other
- concurrent backend processes?
+ users?
- No. That has been handled by the backends.
+ No. This is handled by the backends.
- 4.17) What is an oid? What is a tid?
+ 4.17) What is an OID? What is a TID?
- Oids are PostgreSQL's answer to unique row ids. Every row that is
- created in PostgreSQL gets a unique oid. All oids generated during
+ OIDs are PostgreSQL's answer to unique row ids. Every row that is
+ created in PostgreSQL gets a unique OID. All OIDs generated during
initdb are less than 16384 (from backend/access/transam.h). All
- user-created oids are equal or greater that this. By default, all
- these oids are unique not only within a table, or database, but unique
+ user-created OIDs are equal to or greater than this. By default, all
+ these OIDs are unique not only within a table or database, but unique
within the entire PostgreSQL installation.
- PostgreSQL uses oids in its internal system tables to link rows
- between tables. These oids can be used to identify specific user rows
- and used in joins. It is recommended you use column type oid to store
- oid values. See the sql(l) manual page to see the other internal
- columns. You can create an index on the oid field for faster access.
+ PostgreSQL uses OIDs in its internal system tables to link rows
+ between tables. These OIDs can be used to identify specific user rows
+ and used in joins. It is recommended you use column type OID to store
+ OID values. You can create an index on the OID field for faster
+ access.
Oids are assigned to all new rows from a central area that is used by
- all databases. If you want to change the oid to something else, or if
- you want to make a copy of the table, with the original oid's, there
+ all databases. If you want to change the OID to something else, or if
+ you want to make a copy of the table, with the original OID's, there
is no reason you can't do it:
CREATE TABLE new_table(old_oid oid, mycol int);
- SELECT INTO new SELECT old_oid, mycol FROM old;
+ SELECT old_oid, mycol INTO new FROM old;
COPY new TO '/tmp/pgtable';
DELETE FROM new;
COPY new WITH OIDS FROM '/tmp/pgtable';
- Tids are used to identify specific physical rows with block and offset
+ OIDs are stored as 4-byte integers, and will overflow at 4 billion. No
+ one has reported this ever happening, and we plan to have the limit
+ removed before anyone does.
+
+ TIDs are used to identify specific physical rows with block and offset
values. Tids change after rows are modified or reloaded. They are used
by index entries to point to physical rows.
* retrieve, select
* replace, update
* append, insert
- * oid, serial value
+ * OID, serial value
* portal, cursor
* range variable, table name, table alias
+ A list of general database terms can be found at:
+ http://www.comptechnews.com/~reaster/dbdesign.html
+
4.19) Why do I get the error "FATAL: palloc failure: memory exhausted?"
It is possible you have run out of virtual memory on your system, or
You need to put BEGIN WORK and COMMIT around any use of a large object
handle, that is, surrounding lo_open ... lo_close.
- Current PostgreSQL enforces the rule by closing large object handles
- at transaction commit, which will be instantly upon completion of the
- lo_open command if you are not inside a transaction. So the first
- attempt to do anything with the handle will draw invalid large obj
- descriptor. So code that used to work (at least most of the time) will
- now generate that error message if you fail to use a transaction.
+ Currently PostgreSQL enforces the rule by closing large object handles
+ at transaction commit. So the first attempt to do anything with the
+ handle will draw invalid large obj descriptor. So code that used to
+ work (at least most of the time) will now generate that error message
+ if you fail to use a transaction.
If you are using a client interface like ODBC you may need to set
auto-commit off.
4.22) How do I create a column that will default to the current time?
Use now():
- CREATE TABLE test (x int, modtime timestamp default now() );
+ CREATE TABLE test (x int, modtime timestamp DEFAULT now() );
4.23) Why are my subqueries using IN so slow?
- Currently, we join subqueries to outer queries by sequential scanning
- the result of the subquery for each row of the outer query. A
- workaround is to replace IN with EXISTS. For example, change:
+ Currently, we join subqueries to outer queries by sequentially
+ scanning the result of the subquery for each row of the outer query. A
+ workaround is to replace IN with EXISTS:
SELECT *
FROM tab
WHERE col1 IN (SELECT col2 FROM TAB2)
dump core?
The problem could be a number of things. Try testing your user-defined
- function in a stand alone test program first.
+ function in a stand-alone test program first.
- 5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
- alloc set! mean?
+ 5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
+ alloc set!" mean?
You are pfree'ing something that was not palloc'ed. Beware of mixing
malloc/free and palloc/pfree.
- 5.3) How can I contribute some nifty new types and functions for
- PostgreSQL?
+ 5.3) How can I contribute some nifty new types and functions to PostgreSQL?
Send your extensions to the pgsql-hackers mailing list, and they will
eventually end up in the contrib/ subdirectory.
This requires wizardry so extreme that the authors have never tried
it, though in principle it can be done.
- 5.5) I have changed a source file. Why does the recompile does not see the
+ 5.5) I have changed a source file. Why does the recompile not see the
change?
The Makefiles do not have the proper dependencies for include files.
- You have to do a make clean and then another make. You have to do a
- make clean and then another make.
+ You have to do a make clean and then another make.
TODO list for PostgreSQL
========================
-Last updated: Thu May 25 12:08:57 EDT 2000
+Last updated: Thu Nov 2 16:16:45 EST 2000
The most recent version of this document can be viewed at
the PostgreSQL web site, http://www.PostgreSQL.org.
-A dash(-) marks changes that will appear in the upcoming 7.0 release.
+A dash(-) marks changes that will appear in the upcoming 7.1 release.
Names in brackets "[]" indicate more detailed information is available in
the directory pgsql/doc/TODO.detail/ under that name.
* SELECT pg_class FROM pg_class generates strange error
* Alter TABLE ADD COLUMN does not honor DEFAULT, add CONSTRAINT
-* Creating index of TIMESTAMP & RELTIME fails, or rename to DATETIME(Thomas)
-* SELECT foo UNION SELECT foo is incorrectly simplified to SELECT foo
+* -Creating index of TIMESTAMP & RELTIME fails, or rename to DATETIME(Thomas)
+* -SELECT foo UNION SELECT foo is incorrectly simplified to SELECT foo
* Unique index on base column not honored on inserts from inherited table
INSERT INTO inherit_table (unique_index_col) VALUES (dup) should fail
[inherit]
-* Be smarter about promoting types when UNION merges different data types
-* redesign INSERT ... SELECT to have two levels of target list
+* -Be smarter about promoting types when UNION merges different data types
+* -redesign INSERT ... SELECT to have two levels of target list
* have INTERSECT/EXCEPT prevent duplicates unless ALL is specified
-* SELECT DISTINCT ON col1 col1 col2 FROM tab1 is broken [distinct]
* SELECT col::DECIMAL(12,10); fails
VIEWS
-* Views containing aggregates sometimes fail(Jan)
+* -Views containing aggregates sometimes fail(Jan)
* Creating view and inheriting the view causes view* to show
duplicates(inherit)
-* Disallow LOCK on view
+* -Disallow LOCK on view(Mark Hollomon)
MISC
* Buffer reference counting bugfixes
* Fix libpq bug that causes it to drop backend error message sent
just before connection closure (ie, any FATAL error message)
-* SELECT ... UNION ... ORDER BY fails when sort expr not in result list
-* SELECT ... UNION ... GROUP BY fails if column types disagree, no type
+* -SELECT ... UNION ... ORDER BY fails when sort expr not in result list
+* -SELECT ... UNION ... GROUP BY fails if column types disagree, no type
promotion occurs
* Modification of pg_class can happen while table in use by
another backend. Might lead to MVCC inside of syscache
-* Permission to UPDATE table allows DELETE also
-* Some database schema's are not dumpable; do dumps in oid order
+* Permission to DELETE table allows UPDATE also
ENHANCEMENTS
------------
URGENT
-* Add OUTER joins, left and right[outer](Thomas, Bruce)
-* Allow long tuples by chaining or auto-storing outside db (TOAST)(Jan)
+* -Add OUTER joins, left and right[outer](Tom, Thomas)
+* -Allow long tuples by chaining or auto-storing outside db (TOAST)(Jan)
* Fix memory leak for expressions[memory](Tom?)
ADMIN
-* More access control over who can create tables and access the database
-* Test syslog functionality
+* More access control over who can create tables and use locks(Karel)
+* -Test syslog functionality
+* Convert remaining fprintf(stderr,...) to elog()
* Allow elog() to return error codes, not just messages
* Allow international error message support and add error codes
-* Add ability to specifiy location of lock/socket files [flock]
-* Unify configuration into one configuration file (Peter E)
-* use setproctitle() if it exists for 'ps' display of status
+* -Unify configuration into one configuration file (Peter E)
+* -use setproctitle() if it exists for 'ps' display of status
+* Prevent initdb from running wrong version of postmaster/postgres
TYPES
* Nchar (as distinguished from ordinary varchar),
* Domain capability
-* Add STDDEV/VARIANCE() function for standard deviation computation/variance
-* Allow compression of large fields or a compressed field type
-* Large objects
- o Fix large object mapping scheme, own typeid or reltype(Peter)
- o Not to stuff everything as files in a single directory, hash dirs
- o Allow large object vacuuming
- o Tables that start with xinv confused to be large objects
+* -Add STDDEV/VARIANCE() function for standard deviation computation/variance
+* -Allow compression of large fields or a compressed field type
+* -Large objects
+ o -Fix large object mapping scheme, own typeid or reltype(Peter)
+ o -Not to stuff everything as files in a single directory, hash dirs
+ o -Allow large object vacuuming
+ o -Tables that start with xinv confused to be large objects
* Add IPv6 capability to INET/CIDR types
+* Fix improper masking of some inet/cidr types [cidr]
* Make a separate SERIAL type?
* Store binary-compatible type information in the system
* Add support for & operator
* Allow LOCALE on a per-column basis, default to ASCII
* Allow nulls in arrays
* Allow arrays to be ORDER'ed
+* Support construction of array result values in expressions
+* Change foreign key constraint for array -> element to mean element
+ in array
* Remove Money type, add money formatting for decimal type
* Declare typein/out functions in pg_proc with a special "C string" data type
* Add non-large-object binary field
* Functions returning sets don't really work right[function]
-* Add hash for int8
+* -Add hash for int8 (Tom)
* SELECT col FROM tab WHERE numeric_col = 10.1 fails
+* Get BIT type working
+* Allow better handling of numeric constants, type conversion [typeconv]
+* Support multiple simultaneous character sets, per SQL92
+* Reject character sequences those are not valid in their charset
+* Make functions more multi-byte aware, i.e. trim()
+* Make n of CHAR(n)/VARCHAR(n) the number of letters, not bytes
+* Update macaddr manufacturer numbers, or remove the function macaddr_manuf()
+* Add btree index support for reltime, tinterval, regproc, bit, varbit
+* Add rtree index support for line, lseg, path, point
VIEWS
-* Allow DISTINCT on views
-* Allow views of aggregate columns
-* Allow views with subselects
+* -Allow DISTINCT on views
+* -Allow views of aggregate columns
+* -Allow views with subselects
+* Create insert, update and delete rules for simple one table views
+* -Change elog for complex view ins|upd|del to "cannot {ins|upd|del}
+* Add the functionality for "with check option" clause of create view
INDEXES
* Allow CREATE INDEX zman_index ON test (date_trunc( 'day', zman ) datetime_ops)
fails index can't store constant parameters
-* Allow SQL function indexes
+* -Allow SQL function indexes
* Add FILLFACTOR to index creation
+* Re-enable partial indexes
+* Allow inherited tables to inherit index
COMMANDS
* ALTER TABLE ADD COLUMN to inherited table put column in wrong place [inherit]
-* Add ALTER TABLE DROP/ALTER COLUMN feature(Peter E)
-* Add ALTER TABLE command to change table ownership
+* -Add ALTER TABLE ALTER COLUMN feature(Peter E)
+* Add ALTER TABLE DROP COLUMN feature [drop]
+* Add ALTER TABLE command to change table ownership (Mark H)
+* Add ALTER FUNCTION
+* Add ALTER TABLE ... DROP CONSTRAINT
+* Add ALTER USER command to change user db attributes
+* Automatically drop constraints/functions when object is dropped
* Allow CLUSTER on all tables at once, and improve CLUSTER, loses NOT
NULL specification, indexes, permissions, etc on table
* Add SIMILAR TO to allow character classes, 'pg_[a-c]%'
* Auto-destroy sequence on DROP of table with SERIAL(Ryan)
-* Allow LOCK TABLE tab1, tab2, tab3 so all tables locked in unison
+* Allow LOCK TABLE tab1, tab2, tab3 so all tables locked in unison [lock]
* Allow INSERT/UPDATE of system-generated oid value for a row
-* Allow ESCAPE '\' at the end of LIKE for ANSI compliance [like]
+* -Allow ESCAPE '\' at the end of LIKE for ANSI compliance (Thomas)
* Rewrite the LIKE handling by rewriting the user string with the
supplied ESCAPE [like]
* Allow RULE recompilation
-* Support UNION/INTERSECT/EXCEPT in sub-selects
-* Allow DELETE and UPDATE to use inheritance using tablename*
+* -Support UNION/INTERSECT/EXCEPT in sub-selects
+* -Allow DELETE and UPDATE to use inheritance
* Allow INSERT INTO my_table VALUES (a, b, c, DEFAULT, x, y, z, ...)
* Allow BINARY option to SELECT, like we do with DECLARE
-
+* MOVE 0 should not move to end of cursor
+* Overhaul ACL (access control) code
+* Allow ORDER BY...LIMIT in INSERT INTO ... SELECT
+* Add SHOW command to display locks
+* Allow INSERT INTO tab (col1, ..) VALUES (val1, ..), (val2, ..)
+
CLIENTS
* Make NULL's come out at the beginning or end depending on the
ORDER BY direction
* Update reltuples from COPY command
+* Allow COPY to specify column names
* fix array handling for ECPG
* add pg_dump option to dump type names as standard ANSI types
+* -make pg_dump dump in oid order, so dependencies are resolved (Philip)
* allow psql \d to show primary and foreign keys
* allow psql \d to show temporary table schema
+* add XML interface capability
+* -Allow dumping of users/groups separately
REFERENTIAL INTEGRITY
* Propagate column or table renaming to foreign key constraints
* Emit a warning at foreign key creation time if no UNIQUE index
exists on referenced primary key attributes
+* Add deferred trigger queue file (Jan)
+* Allow oid to act as a foreign key
EXOTIC FEATURES
* Add sql3 recursive unions
-* Add the concept of dataspaces
-* Add replication of distributed databases
+* Add the concept of dataspaces/tablespaces [tablespaces]
+* Add replication of distributed databases [replication]
* Allow queries across multiple databases
* Allow nested transactions (Vadim)
+* Allow INSERT/UPDATE to return new.col or old.col (Philip)
+* SQL*Net listener that makes PostgreSQL appear as an Oracle database
+ to clients
MISC
with after-row images(Vadim) [logging](Vadim)(in-progress)
* Populate backend status area and write program to dump status data
* Make oid use unsigned int more reliably, pg_atoi()
-* Put sort files, large objects in their own directory
+* Put sort files in their own directory
* Do autocommit so always in a transaction block(?)
* Show location of syntax error in query [yacc]
-* Redesign the function call interface to handle NULLs better[function](Tom)
+* -Redesign the function call interface to handle NULLs better[function](Tom)
* Missing optimizer selectivities for date, r-tree, etc. [optimizer]
* Overhaul bufmgr/lockmgr/transaction manager
* Allow BLCKSZ <= 64k, not <= 32k
-* redesign UNION structures to have separarate target lists
-* Allow multi-level query trees for INSERT INTO ... SELECT
+* -redesign UNION structures to have separarate target lists
+* -Allow multi-level query trees for INSERT INTO ... SELECT
* Use IPC_EXCL when creating shared memory and semaphores
* have pg_upgrade use pg_ctl to stop/start postmaster
* Encrpyt passwords in pg_shadow table using MD5
+* Use flock() to prevent multiple postmasters on the same port [flock]
PERFORMANCE
-----------
-FSYNC
+-FSYNC
-* Allow transaction commits with rollback with no-fsync performance [fsync](Vadim)
+* -Allow transaction commits with rollback with no-fsync performance
+ (Vadim)
INDEXES
-* Use indexes in ORDER BY for min(), max()
+* Use indexes to find min() and max()
* Use index to restrict rows returned by multi-key index when used with
non-consecutive keys or OR clauses, so fewer heap accesses
* Allow SELECT * FROM tab WHERE int2col = 4 use int2col index, int8,
float4, numeric/decimal too [optimizer]
* Include heap CTID in btree index keys, remove equal-key cruft from btree
+* Use indexes with CIDR '<<' (contains) operator
+* Fix LIKE indexing optimization for non-ASCII locales
CACHE
-* Cache most recent query plan(s) [prepare]
+* Cache most recent query plan(s) (Karel) [prepare]
* Shared catalog cache, reduce lseek()'s by caching table size in shared area
MISC
* Improve Subplan list handling
* Allow Subplans to use efficient joins(hash, merge) with upper variable
[subquery]
-* use fmgr_info()/fmgr_faddr() instead of fmgr() calls in high-traffic
+* -use fmgr_info()/fmgr_faddr() instead of fmgr() calls in high-traffic
places, like GROUP BY, UNIQUE, index processing, etc.
* improve dynamic memory allocation by introducing tuple-context memory
allocation [memory]
-* In WHERE tab1.x=3 AND tab1.x=tab2.y, add tab2.y=3
+* -In WHERE tab1.x=3 AND tab1.x=tab2.y, add tab2.y=3
* Allow persistent backends [persistent]
* prevent labels from being output for stored rules (Tom)
* allow configuration of maximum number of open files
* Remove pg_listener index
-* Remove ANALYZE from VACUUM so it can be run separately without locks
-* Gather more accurate statistics using indexes
+* -Redesign ANALYZE in VACUUM so it can be run separately without locks
+* Make ANALYZE a separate command
+* Gather more accurate dispersion statistics using indexes
+* Keep statistics about clustering of table rows [optimizer]
+* Improve statistics storage in pg_class [performance]
+* Improve VACUUM speed with indexes [vacuum]
+* Reduce VACUUM lock time by moving tuples with read lock, then write
+ lock and truncate table [vacuum]
+* -BSD/OS does not support locale because there is no LC_MESSAGES (Bruce)
+* Add connection pooling [pool]
SOURCE CODE
-----------
* Add use of 'const' for variables in source tree
-* Fix C optimizer problem where fmgr_ptr calls return different types [alpha]
+* -Fix C optimizer problem where fmgr_ptr calls return different types (Tom)
* Does Mariposa source contain any other bug fixes?
* Remove SET KSQO option now that OR processing is improved(Tom)
-* Use macros to define NT open() file parameters, remove NT-specific defines
-* Change CURRENT to OLD internally for rules
-* rename pl/tcl to pl/pltcl
+* -Use macros to define NT open() file parameters, remove NT-specific defines
+* -Change CURRENT to OLD internally for rules (Bruce)
+* replace the use of fprint(stderr, ...) with elog() in backend code
---------------------------------------------------------------------------
-
-
Frequently Asked Questions (FAQ) for PostgreSQL
</H1>
<P>
-Last updated: Tue Mar 21 16:09:11 EST 2000
+Last updated: Tue Oct 17 00:21:20 EDT 2000
<P>
Current maintainer: Bruce Momjian (<A
-The most recent version of this document can be viewed at the postgreSQL
-Web site, <A HREF="http://www.Postgresql.org">http://www.PostgreSQL.org</A>.<P>
+The most recent version of this document can be viewed at
+<A HREF="http://www.Postgresql.org/docs/faq-english.html">
+http://www.PostgreSQL.org/docs/faq-english.html</A>.<P>
-Linux-specific questions are answered in <A
-HREF="http://www.PostgreSQL.org/docs/faq-linux.html">http://www.PostgreSQL.org/docs/faq-linux.html</A>.<P>
-
-Irix-specific questions are answered in <A
-HREF="http://www.PostgreSQL.org/docs/faq-irix.html">http://www.PostgreSQL.org/docs/faq-irix.html</A>.<P>
-
-HPUX-specific questions are answered in <A
-HREF="http://www.PostgreSQL.org/docs/faq-hpux.shtml">http://www.PostgreSQL.org/docs/faq-hpux.shtml</A>.<P>
+Platform-specific questions are answered at <A
+HREF="http://www.PostgreSQL.org/docs/">http://www.PostgreSQL.org/docs/</A>.<P>
<HR><P>
<H2><CENTER>General Questions</CENTER></H2>
-<A HREF="#1.1">1.1</A>) What is PostgreSQL?<BR>
-<A HREF="#1.2">1.2</A>) What's the copyright on PostgreSQL?<BR>
-<A HREF="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR>
+<A HREF="#1.1">1.1</A>) What is PostgreSQL?<BR>
+<A HREF="#1.2">1.2</A>) What's the copyright on PostgreSQL?<BR>
+<A HREF="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR>
<A HREF="#1.4">1.4</A>) What non-unix ports are available?<BR>
-<A HREF="#1.5">1.5</A>) Where can I get PostgreSQL?<BR>
-<A HREF="#1.6">1.6</A>) Where can I get support for PostgreSQL?<BR>
-<A HREF="#1.7">1.7</A>) What is the latest release of PostgreSQL?<BR>
-<A HREF="#1.8">1.8</A>) What documentation is available for PostgreSQL?<BR>
-<A HREF="#1.9">1.9</A>) How do I find out about known bugs or missing features?<BR>
-<A HREF="#1.10">1.10</A>) How can I learn SQL?<BR>
-<A HREF="#1.11">1.11</A>) Is PostgreSQL Y2K compliant?<BR>
-<A HREF="#1.12">1.12</A>) How do I join the development team?<BR>
-<A HREF="#1.13">1.13</A>) How do I submit a bug report?<BR>
-<A HREF="#1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?<BR>
+<A HREF="#1.5">1.5</A>) Where can I get PostgreSQL?<BR>
+<A HREF="#1.6">1.6</A>) Where can I get support?<BR>
+<A HREF="#1.7">1.7</A>) What is the latest release?<BR>
+<A HREF="#1.8">1.8</A>) What documentation is available?<BR>
+<A HREF="#1.9">1.9</A>) How do I find out about known bugs or missing features?<BR>
+<A HREF="#1.10">1.10</A>) How can I learn SQL?<BR>
+<A HREF="#1.11">1.11</A>) Is PostgreSQL Y2K compliant?<BR>
+<A HREF="#1.12">1.12</A>) How do I join the development team?<BR>
+<A HREF="#1.13">1.13</A>) How do I submit a bug report?<BR>
+<A HREF="#1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?<BR>
<H2><CENTER>User Client Questions</CENTER></H2>
-<A HREF="#2.1">2.1</A>) Are there ODBC drivers for
+<A HREF="#2.1">2.1</A>) Are there ODBC drivers for
PostgreSQL?<BR>
-<A HREF="#2.2">2.2</A>) What tools are available for hooking
+<A HREF="#2.2">2.2</A>) What tools are available for hooking
PostgreSQL to Web pages?<BR>
-<A HREF="#2.3">2.3</A>) Does PostgreSQL have a graphical user interface?
+<A HREF="#2.3">2.3</A>) Does PostgreSQL have a graphical user interface?
A report generator? An embedded query language interface?<BR>
-<A HREF="#2.4">2.4</A>) What languages are available to communicate
+<A HREF="#2.4">2.4</A>) What languages are available to communicate
with PostgreSQL?<BR>
<H2><CENTER>Administrative Questions</CENTER></H2>
-<A HREF="#3.1">3.1</A>) Why does initdb fail?<BR>
-<A HREF="#3.2">3.2</A>) How do I install PostgreSQL somewhere other than
-/usr/local/pgsql?<BR>
-<A HREF="#3.3">3.3</A>) When I start the postmaster, I get a
+<A HREF="#3.1">3.1</A>) Why does <I>initdb</I> fail?<BR>
+<A HREF="#3.2">3.2</A>) How do I install PostgreSQL somewhere other than
+<I>/usr/local/pgsql?</I><BR>
+<A HREF="#3.3">3.3</A>) When I start the <i>postmaster</i>, I get a
<I>Bad System Call</I> or core dumped message. Why?<BR>
-<A HREF="#3.4">3.4</A>) When I try to start the postmaster, I get
-<I>IpcMemoryCreate</I> errors3. Why?<BR>
-<A HREF="#3.5">3.5</A>) When I try to start the postmaster, I get
+<A HREF="#3.4">3.4</A>) When I try to start the <i>postmaster</i>, I get
+<I>IpcMemoryCreate</I> errors. Why?<BR>
+<A HREF="#3.5">3.5</A>) When I try to start the <i>postmaster</i>, I get
<I>IpcSemaphoreCreate</I> errors. Why?<BR>
-<A HREF="#3.6">3.6</A>) How do I prevent other hosts from accessing my
+<A HREF="#3.6">3.6</A>) How do I prevent other hosts from accessing my
PostgreSQL database?<BR>
-<A HREF="#3.7">3.7</A>) Why can't I connect to my database from
+<A HREF="#3.7">3.7</A>) Why can't I connect to my database from
another machine?<BR>
-<A HREF="#3.8">3.8</A>) Why can't I access the database as the
+<A HREF="#3.8">3.8</A>) Why can't I access the database as the
<I>root</I> user?<BR>
-<A HREF="#3.9">3.9</A>) All my servers crash under concurrent
+<A HREF="#3.9">3.9</A>) All my servers crash under concurrent
table access. Why?<BR>
-<A HREF="#3.10">3.10</A>) How do I tune the database engine for
+<A HREF="#3.10">3.10</A>) How do I tune the database engine for
better performance?<BR>
-<A HREF="#3.11">3.11</A>) What debugging features are available in
-PostgreSQL?<BR>
-<A HREF="#3.12">3.12</A>) I get 'Sorry, too many clients' when trying to
+<A HREF="#3.11">3.11</A>) What debugging features are available?<BR>
+<A HREF="#3.12">3.12</A>) I get <I>"Sorry, too many clients"</I> when trying to
connect. Why?<BR>
-<A HREF="#3.13">3.13</A>) What are the pg_psort.XXX files in my
+<A HREF="#3.13">3.13</A>) What are the <I>pg_sorttempNNN.NN</I> files in my
database directory?<BR>
-<A HREF="#3.14">3.14</A>) How do I set up a pg_group?<BR>
<H2><CENTER>Operational Questions</CENTER></H2>
-<A HREF="#4.1">4.1</A>) The system seems to be confused about commas,
+<A HREF="#4.1">4.1</A>) Why is the system confused about commas,
decimal points, and date formats.<BR>
-<A HREF="#4.2">4.2</A>) What is the exact difference between
+<A HREF="#4.2">4.2</A>) What is the exact difference between
binary cursors and normal cursors?<BR>
-<A HREF="#4.3">4.3</A>) How do I <I>select</I> only the first few rows of
+<A HREF="#4.3">4.3</A>) How do I <small>SELECT</small> only the first few rows of
a query?<BR>
-<A HREF="#4.4">4.4</A>) How do I get a list of tables, or other
+<A HREF="#4.4">4.4</A>) How do I get a list of tables or other
things I can see in <I>psql?</I><BR>
-<A HREF="#4.5">4.5</A>) How do you remove a column from a table?<BR>
+<A HREF="#4.5">4.5</A>) How do you remove a column from a table?<BR>
-<A HREF="#4.6">4.6</A>) What is the maximum size for a
+<A HREF="#4.6">4.6</A>) What is the maximum size for a
row, table, database?<BR>
-<A HREF="#4.7">4.7</A>) How much database disk space is required
-to store data from a typical flat file?<BR>
+<A HREF="#4.7">4.7</A>) How much database disk space is required
+to store data from a typical text file?<BR>
-<A HREF="#4.8">4.8</A>) How do I find out what indices or
+<A HREF="#4.8">4.8</A>) How do I find out what indices or
operations are defined in the database?<BR>
-<A HREF="#4.9">4.9</A>) My queries are slow or don't make use of the
+<A HREF="#4.9">4.9</A>) My queries are slow or don't make use of the
indexes. Why?<BR>
-<A HREF="#4.10">4.10</A>) How do I see how the query optimizer is
+<A HREF="#4.10">4.10</A>) How do I see how the query optimizer is
evaluating my query?<BR>
-<A HREF="#4.11">4.11</A>) What is an R-tree index?<BR>
-<A HREF="#4.12">4.12</A>) What is Genetic Query Optimization?<BR>
+<A HREF="#4.11">4.11</A>) What is an R-tree index?<BR>
+<A HREF="#4.12">4.12</A>) What is Genetic Query Optimization?<BR>
-<A HREF="#4.13">4.13</A>) How do I do regular expression searches
-and case-insensitive regexp searching?<BR>
-<A HREF="#4.14">4.14</A>) In a query, how do I detect if a field
+<A HREF="#4.13">4.13</A>) How do I do regular expression searches
+and case-insensitive regular expression searches?<BR>
+<A HREF="#4.14">4.14</A>) In a query, how do I detect if a field
is NULL?<BR>
-<A HREF="#4.15">4.15</A>) What is the difference between the
+<A HREF="#4.15">4.15</A>) What is the difference between the
various character types?<BR>
-<A HREF="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR>
-<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a serial insert?<BR>
-<A HREF="#4.16.3">4.16.3</A>) Wouldn't use of currval() and nextval() lead to a race condition with other concurrent backend processes?<BR>
-
-<A HREF="#4.17">4.17</A>) What is an oid? What is a tid?<BR>
-<A HREF="#4.18">4.18</A>) What is the meaning of some of the terms
+<A HREF="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR>
+<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a
+<small>SERIAL</small> insert?<BR>
+<A HREF="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a
+race condition with other users?<BR>
+
+<A HREF="#4.17">4.17</A>) What is an <small>OID</small>? What is a
+<small>TID</small>?<BR>
+<A HREF="#4.18">4.18</A>) What is the meaning of some of the terms
used in PostgreSQL?<BR>
-<A HREF="#4.19">4.19</A>) Why do I get the error "FATAL: palloc
-failure: memory exhausted?"<BR>
-<A HREF="#4.20">4.20</A>) How do I tell what PostgreSQL version I
+<A HREF="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
+failure: memory exhausted?"</I><BR>
+<A HREF="#4.20">4.20</A>) How do I tell what PostgreSQL version I
am running? <BR>
-<A HREF="#4.21">4.21</A>) My large-object operations get <I>invalid
+<A HREF="#4.21">4.21</A>) My large-object operations get <I>invalid
large obj descriptor.</I> Why?<BR>
<A HREF="#4.22">4.22</A>) How do I create a column that will default to the
current time?<BR>
-<A HREF="#4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so slow?<BR>
+<A HREF="#4.23">4.23</A>) Why are my subqueries using
+<CODE><small>IN</small></CODE> so slow?<BR>
+<A HREF="#4.24">4.24</A>) How do I do an <i>outer</i> join?<BR>
<H2><CENTER>Extending PostgreSQL</CENTER></H2>
-<A HREF="#5.1">5.1</A>) I wrote a user-defined function. When I run
-it in <I>psql,</I> why does it dumps core?<BR>
-<A HREF="#5.2">5.2</A>) What does the message:
-<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?<BR>
-<A HREF="#5.3">5.3</A>) How can I contribute some nifty new types and functions
-for PostgreSQL?<BR>
-<A HREF="#5.4">5.4</A>) How do I write a C function to return a
+<A HREF="#5.1">5.1</A>) I wrote a user-defined function. When I run
+it in <I>psql,</I> why does it dump core?<BR>
+<A HREF="#5.2">5.2</A>) What does the message
+<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?<BR>
+<A HREF="#5.3">5.3</A>) How can I contribute some nifty new types and functions
+to PostgreSQL?<BR>
+<A HREF="#5.4">5.4</A>) How do I write a C function to return a
tuple?<BR>
-<A HREF="#5.5">5.5</A>) I have changed a source file. Why does the
-recompile does not see the change?<BR>
+<A HREF="#5.5">5.5</A>) I have changed a source file. Why does the
+recompile not see the change?<BR>
<HR>
<H2><CENTER>General Questions</CENTER></H2>
<H4><A
-NAME="1.1">1.1</A>)
What is PostgreSQL?</H4><P>
+NAME="1.1">1.1</A>) What is PostgreSQL?</H4><P>
PostgreSQL is an enhancement of the POSTGRES database management system,
a next-generation DBMS research prototype. While PostgreSQL retains the
PostQuel query language with an extended subset of SQL. PostgreSQL is
free and the complete source is available.<P>
-PostgreSQL development is being performed by a team of Internet
+PostgreSQL development is performed by a team of Internet
developers who all subscribe to the PostgreSQL development mailing list.
The current coordinator is Marc G. Fournier (<A
-HREF="mailto:scrappy@postgreSQL.org">scrappy@postgreSQL.org</A>). (See
-below on how to join). This team is now responsible for all current and
-
future development of PostgreSQL.<P>
+HREF="mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See
+below on how to join). This team is now responsible for all development
+of PostgreSQL.<P>
The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
-others have contributed to the porting, testing, debugging and
+others have contributed to the porting, testing, debugging, and
enhancement of the code. The original Postgres code, from which
PostgreSQL is derived, was the effort of many graduate students,
undergraduate students, and staff programmers working under the
It is pronounced <I>Post-Gres-Q-L.</I>
-<H4><A NAME="1.2">1.2</A>) What's the copyright on
+<H4><A NAME="1.2">1.2</A>) What's the copyright on
PostgreSQL?</H4><P>
-PostgreSQL is subject to the following COPYRIGHT
.<P>
+PostgreSQL is subject to the following COPYRIGHT
:<P>
PostgreSQL Data Base Management System<P>
-<H4><A NAME="1.3">1.3</A>) What Unix platforms does PostgreSQL run
+<H4><A NAME="1.3">1.3</A>) What Unix platforms does PostgreSQL run
on?</H4><P>
The authors have compiled and tested PostgreSQL on the following
</UL>
<P>
-<H4><A NAME="1.4">1.4</A>) What non-unix ports are available?</H4><P>
+<H4><A NAME="1.4">1.4</A>) What non-unix ports are available?</H4><P>
-It is possible to compile the libpq C library, psql, and other
+It is possible to compile the <I>libpq</I> C library, psql, and other
interfaces and binaries to run on MS Windows platforms. In this case,
the client is running on MS Windows, and communicates via TCP/IP to a
server running on one of our supported Unix platforms.<P>
A file <I>win31.mak</I> is included in the distribution for making a
-Win32 libpq library and psql.<P>
-
-The database server is now working on Windows NT using the Cygnus
-Unix/NT porting library. See pgsql/doc/README.NT in the distribution.<P>
-There is also a web page at <A HREF=
-"http://www.freebsd.org/~kevlo/postgres/portNT.html">
-http://www.freebsd.org/~kevlo/postgres/portNT.html.</A>
+Win32 <I>libpq</I> library and psql.<P>
-There is another port using U/Win at <A HREF=
-"http://surya.wipro.com/uwin/ported.html">http://surya.wipro.com/uwin/ported.html.</A>
+The database server is now working on Windows NT using Cygwin, the
+Cygnus Unix/NT porting library. See <I>pgsql/doc/FAQ_NT</I> in the
+distribution. It does not work on MS Windows 9X because Cygwin does not
+support the features we need on those platforms. <P>
-<H4><A NAME="1.5">1.5</A>) Where can I get PostgreSQL?</H4><P>
+<H4><A NAME="1.5">1.5</A>) Where can I get PostgreSQL?</H4><P>
The primary anonymous ftp site for PostgreSQL is
<A
-HREF="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</A>
-<P>
-For mirror sites, see our main web site.
+HREF="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A>.
+For mirror sites, see our main Web site.
-<H4><A NAME="1.6">1.6</A>) Where can I get support
for PostgreSQL?</H4><P>
+<H4><A NAME="1.6">1.6</A>) Where can I get support?</H4><P>
-There is no official support for PostgreSQL from the University of
+There is no support for PostgreSQL from the University of
California, Berkeley. It is maintained through volunteer effort.<P>
The main mailing list is: <A
-HREF="mailto:pgsql-general@postgreSQL.org">pgsql-general@postgreSQL.org</A>.
+HREF="mailto:pgsql-general@PostgreSQL.org">pgsql-general@PostgreSQL.org</A>.
It is available for discussion of matters pertaining to PostgreSQL.
-To subscribe, send a mail with the lines in the body (not
+To subscribe, send mail with the following lines in the body (not
the subject line)
<PRE>
</PRE><P>
to <A
-HREF="mailto:pgsql-general-request@
postgreSQL.org">pgsql-general-request@postgreSQL.org</A>.<P>
+HREF="mailto:pgsql-general-request@
PostgreSQL.org">pgsql-general-request@PostgreSQL.org</A>.<P>
There is also a digest list available. To subscribe to this list, send
-email to: <A HREF="mailto:pgsql-general-digest-request@postgreSQL.org">
-pgsql-general-digest-request@postgreSQL.org</A> with a BODY of:
+email to: <A HREF="mailto:pgsql-general-digest-request@PostgreSQL.org">
+pgsql-general-digest-request@PostgreSQL.org</A> with a body of:
<PRE>
subscribe
The bugs mailing list is available. To subscribe to this list, send email
to <A
<PRE>
subscribe
There is also a developers discussion mailing list available. To
subscribe to this list, send email to <A
<PRE>
subscribe
via the PostgreSQL WWW home page at:
<BLOCKQUOTE>
-<A HREF="http://postgreSQL.org">http://postgreSQL.org</A>
+<A HREF="http://www.PostgreSQL.org">http://www.PostgreSQL.org</A>
</BLOCKQUOTE><P>
-There is also an IRC channel on EFNet, channel #PostgreSQL.
+There is also an IRC channel on EFNet, channel <I>#PostgreSQL.</I>
I use the unix command <CODE>irc -c '#PostgreSQL' "$USER"
-irc.phoenix.net</CODE><P>
+irc.phoenix.net
.</CODE><P>
Commercial support for PostgreSQL is available at <A
-HREF="http://www.pgsql.com">http://www.pgsql.com/</A><P>
+HREF="http://www.pgsql.com">http://www.pgsql.com/</A>
.<P>
-<H4><A NAME="1.7">1.7</A>) What is the latest release
of PostgreSQL?</H4><P>
+<H4><A NAME="1.7">1.7</A>) What is the latest release?</H4><P>
-The latest release of PostgreSQL is version 7.0.<P>
+The latest release of PostgreSQL is version 7.0.
2.<P>
We plan to have major releases every four months.<P>
-<H4><A NAME="1.8">1.8</A>) What documentation is available
for PostgreSQL?</H4><P>
+<H4><A NAME="1.8">1.8</A>) What documentation is available?</H4><P>
Several manuals, manual pages, and some small test examples are
-included in the distribution. See the /doc directory. You can also
-browse the manual on-line at <A
-HREF="http://www.postgresql.org/docs/postgres">
-http://www.postgresql.org/docs/postgres.</A>
-in the distribution.
+included in the distribution. See the <I>/doc</I> directory. You can also
+browse the manual online at <A
+HREF="http://www.PostgreSQL.org/docs/postgres">
+http://www.PostgreSQL.org/docs/postgres</A>.
<P>
+There is a PostgreSQL book available at <A
+HREF="http://www.PostgreSQL.org/docs/awbook.html">
+http://www.PostgreSQL.org/docs/awbook.html</A>.<P>
+
<I>psql</I> has some nice \d commands to show information about types,
operators, functions, aggregates, etc.<P>
-
The web site contains even more documentation.<P>
+
Our Web site contains even more documentation.<P>
-<H4><A NAME="1.9">1.9</A>) How do I find out about known bugs or missing features?
+<H4><A NAME="1.9">1.9</A>) How do I find out about known bugs or missing features?
</H4><P>
PostgreSQL supports an extended subset of SQL-92. See our
-<A HREF="http://www.postgreSQL.org/docs/todo.html">
-TODO</A> for a list of known bugs, missing features, and future plans.<P>
+<A HREF="http://www.PostgreSQL.org/docs/todo.html">
+TODO</A> list for known bugs, missing features, and future plans.<P>
+
+<H4><A NAME="1.10">1.10</A>) How can I learn SQL?</H4><P>
-<H4><A NAME="1.10">1.10</A>) How can I learn SQL?</H4><P>
+The PostgreSQL book at <A
+HREF="http://www.PostgreSQL.org/docs/awbook.html">
+http://www.PostgreSQL.org/docs/awbook.html</A> teaches SQL.
There is a nice tutorial at <A
HREF="http://w3.one.net/~jhoffman/sqltut.htm">
HREF="http://members.tripod.com/er4ebus/sql/index.htm">
http://members.tripod.com/er4ebus/sql/index.htm </A><P>
-Many of our users like <I>The Practical SQL Handbook</I>, Bowman et al.,
-Addison Wesley. Others like <I>Lan Times Guide to SQL</I>, Groff et al.,
+Many of our users like <I>The Practical SQL Handbook</I>, Bowman, Judith
+S., et al., Addison-Wesley. Others like <I>The Complete Reference
+
SQL</I>, Groff et al., McGraw-Hill.<P>
-<H4><A NAME="1.11">1.11</A>)
Is PostgreSQL Y2K compliant?</H4><P>
+<H4><A NAME="1.11">1.11</A>) Is PostgreSQL Y2K compliant?</H4><P>
Yes, we easily handle dates past the year 2000AD, and before 2000BC.<P>
-<H4><A NAME="1.12">1.12</A>)
How do I join the development team?</H4><P>
+<H4><A NAME="1.12">1.12</A>) How do I join the development team?</H4><P>
-First, download the latest sources and read the PostgreSQL Developers
-documentation on our web site, or in the distribution.
-Second, subscribe to the pgsql-hackers and pgsql-patches mailing lists.
+First, download the latest source and read the PostgreSQL Developers
+documentation on our Web site, or in the distribution.
+Second, subscribe to the <I>pgsql-hackers</I> and <I>pgsql-patches</I> mailing lists.
Third, submit high-quality patches to pgsql-patches.<P>
-There are about a dozen people who have <SMALL>COMMIT</SMALL> privileges to
-the PostgreSQL CVS archive. All of them have submitted so many
-high-quality patches that it was a pain for the existing
+There are about a dozen people who have commit privileges to
+the PostgreSQL CVS archive. They each have submitted so many
+high-quality patches that it was impossible for the existing
committers to keep up, and we had confidence that patches they
-committed were likely to be of high quality.
+committed were of high quality.
-<H4><A NAME="1.13">1.13</A>)
How do I submit a bug report?</H4><P>
+<H4><A NAME="1.13">1.13</A>) How do I submit a bug report?</H4><P>
Fill out the "bug-template" file and send it to: <A
Also check out our ftp site <A
-HREF="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</A> to
+HREF="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to
see if there is a more recent PostgreSQL version or patches.<P>
-<H4><A NAME="1.14">1.14</A>) How does PostgreSQL compare to other
+<H4><A NAME="1.14">1.14</A>) How does PostgreSQL compare to other
DBMS's?</H4><P>
There are several ways of measuring software: features, performance,
<DD>
PostgreSQL has most features present in large commercial DBMS's, like
-transactions, subselects, triggers, views, and sophisticated locking.
-We have some features they don't have, like user-defined types,
-inheritance, rules, and multi-version concurrency control to reduce lock
-contention. We don't have foreign key referential integrity or outer
-joins, but are working on them for our next release.<BR><BR>
+transactions, subselects, triggers, views, foreign key referential
+integrity, and sophisticated locking. We have some features they don't
+have, like user-defined types, inheritance, rules, and multi-version
+concurrency control to reduce lock contention. We don't have outer
+joins, but are working on them.<BR><BR>
<DT> <B>Performance</B>
<DD>
commercial databases, though in this mode, an OS crash could cause data
corruption. We are working to provide an intermediate mode that suffers
less performance overhead than full fsync mode, and will allow data
-integrity within 30 seconds of an OS crash. The mode is select-able by
-the database administrator.<BR><BR>
+integrity within 30 seconds of an OS crash.<BR><BR>
In comparison to MySQL or leaner database systems, we are slower on
inserts/updates because we have transaction overhead. Of course, MySQL
doesn't have any of the features mentioned in the <I>Features</I>
section above. We are built for flexibility and features, though we
continue to improve performance through profiling and source code
-analysis. There is an interesting web page comparing PostgreSQL to MySQL
+analysis. There is an interesting Web page comparing PostgreSQL to MySQL
at <a href="http://openacs.org/why-not-mysql.html">
http://openacs.org/why-not-mysql.html</a><BR><BR>
in our BSD-style license stated above.<BR><BR>
</DL>
-
<HR>
<H2><CENTER>User Client Questions</CENTER></H2>
-<H4><A NAME="2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?</H4><P>
+<H4><A NAME="2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?</H4><P>
-There are two ODBC drivers available, P
ostODBC and OpenLink ODBC.<P>
+There are two ODBC drivers available, P
sqlODBC and OpenLink ODBC.<P>
-PostODBC is included in the distribution. More information about it can
-be gotten from: <A HREF="http://www.insightdist.com/psqlodbc">
-
http://www.insightdist.com/psqlodbc</A><P>
+PsqlODBC is included in the distribution. More information about it can
+be gotten from <A HREF="ftp://ftp.PostgreSQL.org/pub/odbc/">
+
ftp://ftp.PostgreSQL.org/pub/odbc/</A>.<P>
OpenLink ODBC can be gotten from <A HREF="http://www.openlinksw.com/">
http://www.openlinksw.com</A>. It works with their standard ODBC client
available. Questions to <A
+See also the <A HREF="http://www.PostgreSQL.org/docs/programmer/odbc.htm">
+ODBC chapter of the Programmer's Guide</A>.<P>
-<H4><A NAME="2.2">2.2</A>) What tools are available for hooking
+<H4><A NAME="2.2">2.2</A>) What tools are available for hooking
PostgreSQL to Web pages?</H4><P>
A nice introduction to Database-backed Web pages can be seen at: <A
There is also one at <A HREF="http://www.phone.net/home/mwm/hotlist/">
http://www.phone.net/home/mwm/hotlist/.</A><P>
-For web integration, PHP is an excellent interface. It is at:
+For Web integration, PHP is an excellent interface. It is at
<A HREF="http://www.php.net">http://www.php.net</A><P>
-PHP is great for simple stuff, but for more complex cases, many
-use the perl interface and CGI.pm.<P>
+For complex cases, many use the Perl interface and CGI.pm.<P>
-A WWW gateway based on WDB using
perl can be downloaded from <A
+A WWW gateway based on WDB using
Perl can be downloaded from <A
HREF="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb-p95</A>
-<H4><A NAME="2.3">2.3</A>) Does PostgreSQL have a graphical user interface?
+<H4><A NAME="2.3">2.3</A>) Does PostgreSQL have a graphical user interface?
A report generator? An embedded query language interface?</H4><P>
We have a nice graphical user interface called <I>pgaccess,</I> which is
shipped as part of the distribution. <I>Pgaccess</I> also has a report
-generator. The
web page is <A HREF=
+generator. The
Web page is <A HREF=
"http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A><P>
We also include <I>ecpg,</I> which is an embedded SQL query language interface for
C.
-<H4><A NAME="2.4">2.4</A>) What languages are available to
+<H4><A NAME="2.4">2.4</A>) What languages are available to
communicate with PostgreSQL?</H4><P>
We have:
<UL>
-<LI>C(libpq)
-<LI>C++(libpq++)
-<LI>Embedded C(ecpg)
-<LI>Java(jdbc)
-<LI>Perl(perl5)
-<LI>ODBC(odbc)
-<LI>Python(PyGreSQL)
-<LI>TCL(libpgtcl)
-<LI>C Easy API(libpgeasy)
-<LI>Embedded HTML(<A HREF="http://www.php.net">PHP from http://www.php.net</A>)
+<LI>C (libpq)
+<LI>C++ (libpq++)
+<LI>Embedded C (ecpg)
+<LI>Java (jdbc)
+<LI>Perl (perl5)
+<LI>ODBC (odbc)
+<LI>Python (PyGreSQL)
+<LI>TCL (libpgtcl)
+<LI>C Easy API (libpgeasy)
+<LI>Embedded HTML
(<A HREF="http://www.php.net">PHP from http://www.php.net</A>)
</UL><P>
<HR>
<H2><CENTER>Administrative Questions</CENTER></H2><P>
-<H4><A NAME="3.1">3.1</A>) Why does
initdb fail?</H4><P>
+<H4><A NAME="3.1">3.1</A>) Why does
<I>initdb</I> fail?</H4><P>
+Try these:
<UL>
<LI> check that you don't have any of the previous version's binaries in
-your path (If you see the message <CODE>WARN:heap_modifytuple: repl is
-\ 9</CODE>, this is the problem.)
-<Li> check to see that you have the proper paths set
+your path
+<LI> check to see that you have the proper paths set
<LI> check that the <I>postgres</I> user owns the proper files
</UL><P>
+If you see an error message about <i>oidvector,</i> you definately have
+a version mismatch.<P>
-<H4><A NAME="3.2">3.2</A>) How do I install PostgreSQL somewhere
-other than
/usr/local/pgsql?</H4><P>
+<H4><A NAME="3.2">3.2</A>) How do I install PostgreSQL somewhere
+other than
<I>/usr/local/pgsql?</I></H4><P>
-The simplest way is to specify the --prefix option when running configure.
-If you forgot to do that, you can edit Makefile.global and change POSTGRESDIR
-accordingly, or create a
Makefile.custom and define POSTGRESDIR there.<P>
+The simplest way is to specify the --prefix option when running <I>configure.</I>
+If you forgot to do that, you can edit <I>Makefile.global</I> and change POSTGRESDIR
+accordingly, or create a
<I>Makefile.custom</I> and define POSTGRESDIR there.<P>
-<H4><A NAME="3.3">3.3</A>) When I start the postmaster, I get a <I>Bad
+<H4><A NAME="3.3">3.3</A>) When I start the <i>postmaster</i>, I get a <I>Bad
System Call</I> or core dumped message. Why?</H4><P>
It could be a variety of problems, but first check to see that you
-have system V extensions installed in your kernel. PostgreSQL requires
+have System V extensions installed in your kernel. PostgreSQL requires
kernel support for shared memory and semaphores.<P>
-<H4><A NAME="3.4">3.4</A>) When I try to start the postmaster, I
+<H4><A NAME="3.4">3.4</A>) When I try to start the <i>postmaster,</i> I
get <I>IpcMemoryCreate</I> errors. Why?</H4><P>
-You either do not have shared memory configured properly in kernel or
+You either do not have shared memory configured properly in your kernel or
you need to enlarge the shared memory available in the kernel. The
exact amount you need depends on your architecture and how many buffers
-and backend processes you configure postmaster to run with.
+and backend processes you configure for the <i>postmaster.</i>
For most systems, with default numbers of buffers and processes, you
need a minimum of ~1MB.<P>
-<H4><A NAME="3.5">3.5</A>) When I try to start the postmaster, I
+<H4><A NAME="3.5">3.5</A>) When I try to start the <i>postmaster,</i> I
get <I>IpcSemaphoreCreate</I> errors. Why?</H4><P>
If the error message is <I>IpcSemaphoreCreate: semget failed (No space
left on device)</I> then your kernel is not configured with enough
semaphores. Postgres needs one semaphore per potential backend process.
-A temporary solution is to start the postmaster with a smaller limit on
+A temporary solution is to start the <i>postmaster</i> with a smaller limit on
the number of backend processes. Use <I>-N</I> with a parameter less
than the default of 32. A more permanent solution is to increase your
kernel's <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.<P>
support configured in your kernel at all.<P>
-<H4><A NAME="3.6">3.6</A>) How do I prevent other hosts from
+<H4><A NAME="3.6">3.6</A>) How do I prevent other hosts from
accessing my PostgreSQL database?</H4><P>
By default, PostgreSQL only allows connections from the local machine
-using unix domain sockets. Other machines will not be able to connect
+using Unix domain sockets. Other machines will not be able to connect
unless you add the <I>-i</I> flag to the <I>postmaster,</I>
<B>and</B> enable host-based authentication by modifying the file
<I>$PGDATA/pg_hba.conf</I> accordingly. This will allow TCP/IP connections.
<P>
-<H4><A NAME="3.7">3.7</A>) Why can't I connect to my database from
+<H4><A NAME="3.7">3.7</A>) Why can't I connect to my database from
another machine?</H4><P>
The default configuration allows only unix domain socket connections
from the local machine. To enable TCP/IP connections, make sure the
-postmaster has been started with the <I>-i</I> option, and add an
+<i>postmaster</i> has been started with the <I>-i</I> option, and add an
appropriate host entry to the file
-<I>pgsql/data/pg_hba.conf</I>. See the <I>pg_hba.conf</I> manual page.<P>
+<I>pgsql/data/pg_hba.conf</I>.
-
-<H4><A NAME="3.8">3.8</A>) Why can't I access the database as the <I>root</I>
+<H4><A NAME="3.8">3.8</A>) Why can't I access the database as the <I>root</I>
user?</H4><P>
You should not create database users with user id 0 (root). They will be
-unable to access the database. This is a security precaution because
-of the ability of any user to dynamically link object modules into the
+unable to access the database. This is a security precaution because
+of the ability of users to dynamically link object modules into the
database engine.<P>
-<H4><A NAME="3.9">3.9</A>) All my servers crash under concurrent
+<H4><A NAME="3.9">3.9</A>) All my servers crash under concurrent
table access. Why?</H4><P>
This problem can be caused by a kernel that is not configured to support
semaphores.<P>
-<H4><A NAME="3.10">3.10</A>) How do I tune the database engine for
+<H4><A NAME="3.10">3.10</A>) How do I tune the database engine for
better performance?</H4><P>
Certainly, indices can speed up queries. The <SMALL>EXPLAIN</SMALL> command
indices are being used.<P>
If you are doing a lot of <SMALL>INSERTs</SMALL>, consider doing them in a large
-batch using the <SMALL>COPY</SMALL> command. This is much faster than single
+batch using the <SMALL>COPY</SMALL> command. This is much faster than
individual <SMALL>INSERTS.</SMALL> Second, statements not in a <SMALL>BEGIN
WORK/COMMIT</SMALL> transaction block are considered to be in their
own transaction. Consider performing several statements in a single
consider dropping and recreating indices when making large data
changes.<P>
-There are several tuning things that can be done. You can disable
-fsync() by starting the postmaster with a <I>-o -F</I> option. This will
-prevent <I>fsync()'s</I> from flushing to disk after every transaction.<P>
+There are several tuning options. You can disable
+<I>fsync()</I> by starting the <I>postmaster</I> with a <I>-o -F</I>
+option. This will prevent <I>fsync()'s</I> from flushing to disk after
+every transaction.<P>
-You can also use the postmaster -B option to increase the number of
+You can also use the <I>postmaster</I> <I>-B</I> option to increase the number of
shared memory buffers used by the backend processes. If you make this
-parameter too high, the postmaster may not start up because you've exceeded
+parameter too high, the <I>postmaster</I> may not start because you've exceeded
your kernel's limit on shared memory space.
Each buffer is 8K and the default is 64 buffers.<P>
-You can also use the backend -S option to increase the maximum amount
-of memory used by the backend process for temporary sorts. The -S value
+You can also use the backend <I>-S</I> option to increase the maximum amount
+of memory used by the backend process for temporary sorts. The <I>-S</I> value
is measured in kilobytes, and the default is 512 (ie, 512K).<P>
-You can also use the <SMALL>CLUSTER</SMALL> command to group data in base tables to
-match an index. See the
cluster(l) manual page for more details.<P>
+You can also use the <SMALL>CLUSTER</SMALL> command to group data in tables to
+match an index. See the
<small>CLUSTER</small> manual page for more details.<P>
-<H4><A NAME="3.11">3.11</A>) What debugging features are available in
-PostgreSQL?</H4><P>
+<H4><A NAME="3.11">3.11</A>) What debugging features are available?</H4><P>
PostgreSQL has several features that report status information that can
be valuable for debugging purposes.<P>
-First, by running configure with the --enable-cassert option, many
+First, by running <I>configure</I> with the --enable-cassert option, many
<I>assert()'s</I> monitor the progress of the backend and halt the program when
something unexpected occurs.<P>
-Both postmaster and postgres have several debug options available.
-First, whenever you start the postmaster, make sure you send the
+Both <I>postmaster</I> and <I>postgres</I> have several debug options available.
+First, whenever you start the <I>postmaster,</I> make sure you send the
standard output and error to a log file, like:
<PRE>
cd /usr/local/pgsql
This will put a server.log file in the top-level PostgreSQL directory.
This file contains useful information about problems or errors
-encountered by the server. Postmaster has a -d option that allows even
-more detailed information to be reported. The -d option takes a number
+encountered by the server. <I>Postmaster</I> has a <I>-d</I> option that allows even
+more detailed information to be reported. The <I>-d</I> option takes a number
that specifies the debug level. Be warned that high debug level values
generate large log files.<P>
-You can actually run the postgres backend from the command line, and
-type your SQL statement directly. This is recommended <B>only</B> for
-debugging purposes. Note that a newline terminates the query, not a
-semicolon. If you have compiled with debugging symbols, you can use a
-debugger to see what is happening. Because the backend was not started
-from the postmaster, it is not running in an identical environment and
-locking/backend interaction problems may not be duplicated. Some
-debuggers can attach to an already-running backend; that is the most
-convenient way to diagnose problems in the normal multi-backend
-environment.
-<P>
-
-The postgres program has -s, -A, and -t options that can be very useful
+If the <i>postmaster</i> is not running, you can actually run the
+<I>postgres</I> backend from the command line, and type your SQL statement
+directly. This is recommended <B>only</B> for debugging purposes. Note
+that a newline terminates the query, not a semicolon. If you have
+compiled with debugging symbols, you can use a debugger to see what is
+happening. Because the backend was not started from the <I>postmaster,</I> it
+is not running in an identical environment and locking/backend
+interaction problems may not be duplicated.<P>
+
+If the <i>postmaster</i> is running, start <I>psql</I> in one window,
+then find the <small>PID</small> of the <i>postgres</i> process used by
+<i>psql.</i> Use a debugger to attach to the <i>postgres</i>
+<small>PID.</small> You can set breakpoints in the debugger and issue
+queries from <i>psql.</i> If you are debugging <i>postgres</i> startup,
+you can set PGOPTIONS="-W n", then start <i>psql.</i> This will cause
+startup to delay for <i>n</i> seconds so you can attach with the
+debugger and trace through the startup sequence.<P>
+
+The <I>postgres</I> program has <I>-s, -A,</I> and <I>-t</I> options that can be very useful
for debugging and performance measurements.<P>
You can also compile with profiling to see what functions are taking
execution time. The backend profile files will be deposited in the
-pgsql/data/base/dbname directory. The client profile file will be put
+<I>pgsql/data/base/dbname</I> directory. The client profile file will be put
in the client's current directory.<P>
<H4><A NAME="3.12">3.12</A>) I get 'Sorry, too many clients' when trying
to connect. Why?</H4><P>
-You need to increase the postmaster's limit on how many concurrent backend
+You need to increase the <i>postmaster's</i> limit on how many concurrent backend
processes it can start.<P>
-In Postgres 6.5 and up, the default limit is 32 processes. You can
-increase it by restarting the postmaster with a suitable <I>-N</I>
+In PostgreSQL 6.5 and up, the default limit is 32 processes. You can
+increase it by restarting the <i>postmaster</i> with a suitable <I>-N</I>
value. With the default configuration you can set <I>-N</I> as large as
-1024; if you need more, increase <SMALL>MAXBACKENDS</SMALL> in
+1024. If you need more, increase <SMALL>MAXBACKENDS</SMALL> in
<I>include/config.h</I> and rebuild. You can set the default value of
-<I>-N</I> at configuration time, if you like, using configure's
+<I>-N</I> at configuration time, if you like, using <I>configure's</I>
<I>--with-maxbackends</I> switch.<P>
Note that if you make <I>-N</I> larger than 32, you must also increase
-<I>-B</I> beyond its default of 64; -B must be at least twice -N, and
+<I>-B</I> beyond its default of 64; <I>-B</I> must be at least twice <I>-N,</I> and
probably should be more than that for best performance. For large
numbers of backend processes, you are also likely to find that you need
to increase various Unix kernel configuration parameters. Things to
check include the maximum size of shared memory blocks,
-<SMALL>SHMMAX,</SMALL> the maximum number of semaphores,
-<SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI,</SMALL> the maximum number of
-processes, <SMALL>NPROC,</SMALL> the maximum number of processes per
-user, <SMALL>MAXUPRC,</SMALL> and the maximum number of open files,
-<SMALL>NFILE</SMALL> and <SMALL>NINODE.</SMALL> The reason that Postgres
-has a limit on the number of allowed backend processes is so that you
-
can ensure that your system won't run out of resources.<P>
-
-In Postgres versions prior to 6.5, the maximum number of backends was
+<SMALL>SHMMAX;</SMALL> the maximum number of semaphores,
+<SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI;</SMALL> the maximum number of
+processes, <SMALL>NPROC;</SMALL> the maximum number of processes per
+user, <SMALL>MAXUPRC;</SMALL> and the maximum number of open files,
+<SMALL>NFILE</SMALL> and <SMALL>NINODE.</SMALL> The reason that PostgreSQL
+has a limit on the number of allowed backend processes is so
+your system won't run out of resources.<P>
+
+In PostgreSQL versions prior to 6.5, the maximum number of backends was
64, and changing it required a rebuild after altering the MaxBackendId
constant in <I>include/storage/sinvaladt.h.</I><P>
-<H4><A NAME="3.13">3.13</A>) What are the pg_tempNNN.NN files in my
+<H4><A NAME="3.13">3.13</A>) What are the <I>pg_sorttempNNN.NN</I> files in my
database directory?</H4><P>
They are temporary files generated by the query executor. For
example, if a sort needs to be done to satisfy an <SMALL>ORDER BY,</SMALL> and
-the sort requires more space than the backend's -S parameter allows,
-then temp files are created to hold the extra data.<P>
+the sort requires more space than the backend's <I>-S</I> parameter allows,
+then temp
orary files are created to hold the extra data.<P>
-The temp files should go away automatically, but might not if a backend
-crashes during a sort. If you have no transactions running at the time,
+The temporary files should be deleted automatically, but might not if a backend
+crashes during a sort. If you have no backends running at the time,
it is safe to delete the pg_tempNNN.NN files.<P>
-<H4><A NAME="3.14">3.14</A>) How do I set up a pg_group?</H4><P>
-
-Currently, there is no easy interface to set up user groups. You have to
-explicitly insert/update the pg_group table. For example:
-
-<PRE>
- jolly=> insert into pg_group (groname, grosysid, grolist)
- jolly=> values ('posthackers', '1234', '{5443, 8261}');
- INSERT 548224
- jolly=> grant insert on foo to group posthackers;
- CHANGE
- jolly=>
-</PRE><P>
-
- The fields in pg_group are:
-<UL>
-<LI>groname: the group name. This a name and should
-be purely alphanumeric. Do not include underscores
-or other punctuation.
-<LI>grosysid: the group id. This is an int4.
-This should be unique for each group.
-<LI>grolist: the list of pg_user id's that belong in the group.
-This is an int4[].
-</UL><P>
-
-
<HR>
<H2><CENTER>Operational Questions</CENTER></H2><P>
-<H4><A NAME="4.1">4.1</A>) The system seems to be confused about
+<H4><A NAME="4.1">4.1</A>) Why is system confused about
commas, decimal points, and date formats.</H4><P>
-Check your locale configuration. PostgreSQL uses the locale settings of
-the user that ran the postmaster process. There are postgres and psql
+Check your locale configuration. PostgreSQL uses the locale setting of
+the user that ran the <i>postmaster</i> process. There are postgres and psql
SET commands to control the date format. Set those accordingly for
your operating environment.<P>
-<H4><A NAME="4.2">4.2</A>) What is the exact difference between
+<H4><A NAME="4.2">4.2</A>) What is the exact difference between
binary cursors and normal cursors?</H4><P>
See the <SMALL>DECLARE</SMALL> manual page for a description.<P>
-<H4><A NAME="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few
+<H4><A NAME="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few
rows of a query?</H4><P>
See the <SMALL>FETCH</SMALL> manual page, or use SELECT ... LIMIT....<P>
or the entire query may have to be evaluated until the desired rows have
been generated.<P>
-<H4><A NAME="4.4">4.4</A>) How do I get a list of tables, or other
-
information I see in <I>psql?</I><BR></H4><P>
+<H4><A NAME="4.4">4.4</A>) How do I get a list of tables or other
+
things I can see in <I>psql?</I><BR></H4><P>
-You can read the source code for <I>psql,</I> file
-pgsql/src/bin/psql/psql.c. It contains SQL commands that generate the
+You can read the source code for <I>psql</I> in file
+<I>pgsql/src/bin/psql/psql.c.</I> It contains SQL commands that generate the
output for psql's backslash commands. You can also start <I>psql</I>
-with the <I>-E</I> option so that it will print out the queries it uses
+with the <I>-E</I> option so it will print out the queries it uses
to execute the commands you give.<P>
-<H4><A NAME="4.5">4.5</A>) How do you remove a column from a
+<H4><A NAME="4.5">4.5</A>) How do you remove a column from a
table?</H4><P>
We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do
-<H4><A NAME="4.6">4.6</A>) What is the maximum size for a
+<H4><A NAME="4.6">4.6</A>) What is the maximum size for a
row, table, database?</H4><P>
-Rows are limited to 8K bytes, but this can be changed by editing
-<I>include/config.h</I> and changing <SMALL>BLCKSZ.</SMALL> To use attributes
-larger than 8K, you can also use the large object interface.<P>
+These are the limits:
+
+<PRE>
+Maximum size for a database? unlimited (60GB databases exist)
+Maximum size for a table? unlimited on all operating systems
+Maximum size for a row? 8k, configurable to 32k
+Maximum number of rows in a table? unlimited
+Maximum number of columns in a table? unlimited
+Maximum number of indexes on a table? unlimited
+</PRE>
+
+Of course, these are not actually unlimited, but limited to available
+disk space.<P>
-Rows do not cross 8k boundaries so a 5k row will require 8k of
-storage.<P>
+To change the maximum row size, edit <I>include/config.h</I> and change
+<SMALL>BLCKSZ.</SMALL> To use attributes larger than 8K, you can also
+use the large object interface.<P>
-Table and database sizes are unlimited. There are many databases that
-are tens of gigabytes, and probably some that are hundreds.
+The row length limit will be removed in 7.1.<P>
-<H4><A NAME="4.7">4.7</A>)How much database disk space is required to
-store data from a typical flat file?<BR></H4><P>
-A Postgres database can require about six and a half times the disk space
+<H4><A NAME="4.7">4.7</A>) How much database disk space is required to
+store data from a typical text file?<BR></H4><P>
+
+A PostgreSQL database may need six-and-a-half times the disk space
required to store the data in a flat file.<P>
Consider a file of 300,000 lines with two integers on each line. The
1755 database pages * 8192 bytes per page = 14,376,960 bytes (14MB)
</PRE></P>
-Indexes do not contain as much overhead, but do contain the data that is
+Indexes do not require as much overhead, but do contain the data that is
being indexed, so they can be large also.<P>
-<H4><A NAME="4.8">4.8</A>) How do I find out what indices or
+<H4><A NAME="4.8">4.8</A>) How do I find out what indices or
operations are defined in the database?</H4><P>
<I>psql</I> has a variety of backslash commands to show such information. Use
the database system tables.<P>
-<H4><A NAME="4.9">4.9</A>) My queries are slow or don't make
+<H4><A NAME="4.9">4.9</A>) My queries are slow or don't make
use of the indexes. Why?</H4><P>
-PostgreSQL does not automatically maintain statistics. One has to make
-an explicit <SMALL>VACUUM</SMALL> call to update the statistics. After
+PostgreSQL does not automatically maintain statistics. V<SMALL>ACUUM</SMALL>
+must be run to update the statistics. After
statistics are updated, the optimizer knows how many rows in the table,
and can better decide if it should use indices. Note that the optimizer
does not use indices in cases when the table is small because a
For column-specific optimization statistics, use <SMALL>VACUUM
ANALYZE.</SMALL> <SMALL>VACUUM ANALYZE</SMALL> is important for complex
-multi-join queries, so the optimizer can estimate the number of rows
+multijoin queries, so the optimizer can estimate the number of rows
returned from each table, and choose the proper join order. The backend
does not keep track of column statistics on its own, so <SMALL>VACUUM
ANALYZE</SMALL> must be run to collect them periodically.<P>
begin with <I>%,</I> and <I>~</I>(regular expression searches) should
start with <I>^.</I>
-<H4><A NAME="4.10">4.10</A>) How do I see how the query optimizer is
+<H4><A NAME="4.10">4.10</A>) How do I see how the query optimizer is
evaluating my query?</H4><P>
See the <SMALL>EXPLAIN</SMALL> manual page.<P>
-<H4><A NAME="4.11">4.11</A>)
What is an R-tree index?</H4><P>
+<H4><A NAME="4.11">4.11</A>) What is an R-tree index?</H4><P>
-An r-tree index is used for indexing spatial data. A hash index can't
+An R-tree index is used for indexing spatial data. A hash index can't
handle range searches. A B-tree index only handles range searches in a
single dimension. R-tree's can handle multi-dimensional data. For
example, if an R-tree index can be built on an attribute of type <I>point,</I>
-the system can more efficient answer queries like select all points
-within a bounding rectangle.<P>
+the system can more efficiently answer queries such as "select all points
+within a bounding rectangle.
"<P>
-The canonical paper that describes the original R-
Tree design is:<P>
+The canonical paper that describes the original R-
tree design is:<P>
-Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching."
+Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching."
Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.<P>
You can also find this paper in Stonebraker's "Readings in Database
-Systems"<P>
-Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
+Built-in R-trees can handle polygons and boxes. In theory, R-trees can
be extended to handle higher number of dimensions. In practice,
-extending R-trees require a bit of work and we don't currently have any
+extending R-trees requires a bit of work and we don't currently have any
documentation on how to do it.<P>
-<H4><A NAME="4.12">4.12</A>) What is Genetic Query
+<H4><A NAME="4.12">4.12</A>) What is Genetic Query
Optimization?</H4><P>
-The GEQO module in PostgreSQL is intended to solve the query
-optimization problem of joining many tables by means of a Genetic
+The GEQO module speeds query
+optimization when joining many tables by means of a Genetic
Algorithm (GA). It allows the handling of large join queries through
-non-exhaustive search.<P>
-
-For further information see the documentation.
-
+nonexhaustive search.<P>
+<H4><A NAME="4.13">4.13</A>) How do I do regular expression searches and
+case-insensitive regular expression searches?</H4><P>
-<H4><A NAME="4.13">4.13</A>) How do I do regular expression searches and
-case-insensitive regexp searching?</H4><P>
-
-The <I>~</I> operator does regular-expression matching, and <I>~*</I>
-does case-insensitive regular-expression matching. There is no
+The <I>~</I> operator does regular expression matching, and <I>~*</I>
+does case-insensitive regular expression matching. There is no
case-insensitive variant of the LIKE operator, but you can get the
effect of case-insensitive <SMALL>LIKE</SMALL> with this:
<PRE>
WHERE lower(textfield) LIKE lower(pattern)
</PRE>
-<H4><A NAME="4.14">4.14</A>) In a query, how do I detect if a field
+<H4><A NAME="4.14">4.14</A>) In a query, how do I detect if a field
is NULL?</H4><P>
You test the column with IS NULL and IS NOT NULL.<P>
-<H4><A NAME="4.15">4.15</A>) What is the difference between the
+<H4><A NAME="4.15">4.15</A>) What is the difference between the
various character types?</H4>
<PRE>
You will see the internal name when examining system catalogs
and in some error messages.<P>
-The last four types above are "varlena" types (i.e. the first four bytes
+The last four types above are "varlena" types (i.e., the first four bytes
are the length, followed by the data). <I>char(#)</I> allocates the
maximum number of bytes no matter how much data is stored in the field.
<I>text, varchar(#),</I> and <I>bytea</I> all have variable length on the disk,
first column of this type.<P>
-<H4><A NAME="4.16.1">4.16.1</A>) How do I create a
+<H4><A NAME="4.16.1">4.16.1</A>) How do I create a
serial/auto-incrementing field?</H4><P>
-PostgreSQL supports <SMALL>SERIAL</SMALL> data type. It auto-creates a
-sequence and index on the column. For example, this...
+PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It auto-creates a
+sequence and index on the column. For example, this:
<PRE>
CREATE TABLE person (
id SERIAL,
name TEXT
);
</PRE>
-...is automatically translated into this...
+is automatically translated into this:
<PRE>
CREATE SEQUENCE person_id_seq;
CREATE TABLE person (
</PRE>
See the <I>create_sequence</I> manual page for more information about sequences.
-You can also use each row's <I>oid</I> field as a unique value. However, if
+You can also use each row's <I>OID</I> field as a unique value. However, if
you need to dump and reload the database, you need to use <I>pg_dump's -o</I>
-option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the
oids.<P>
+option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the
<small>OID</small>s.<P>
-For more details, see Bruce Momjian's chapter on
-<A HREF="http://www.postgresql.org/docs/aw_pgsql_book/node74.html">Numbering Rows.</A>
+<A HREF="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering Rows.</A>
-<H4><A NAME="4.16.2">4.16.2</A>) How do I get the back the generated SERIAL value after an insert?</H4><P>
-Probably the simplest approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A HREF="#4.16.1">4.16.1</A>, that might look like this:
+<H4><A NAME="4.16.2">4.16.2</A>) How do I get the value of a
+<small>SERIAL</small> insert?</H4><P>
+One approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A HREF="#4.16.1">4.16.1</A>, that might look like this:
<PRE>
$newSerialID = nextval('person_id_seq');
INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
</PRE>
-You would then also have the new value stored in <CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign key to the <CODE>person</CODE> table). Note that the name of the automatically-created SEQUENCE object will be named <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I> are the names of your table and your SERIAL column, respectively.
+
+You would then also have the new value stored in
+<CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign
+key to the <CODE>person</CODE> table). Note that the name of the
+automatically created SEQUENCE object will be named
+<<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where
+<I>table</I> and <I>serialcolumn</I> are the names of your table and
+your SERIAL column, respectively.
+
<P>
-Similarly, you could retrieve the just-assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,
+Alternatively, you could retrieve the assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,
<PRE>
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
</PRE>
-Finally, you could use the <A HREF="#4.17">oid</A> returned from the INSERT statement to lookup the default value, though this is probably the least portable approach. In perl, using DBI with Edmund Mergl's DBD::Pg module, the oid value is made available via $sth->{pg_oid_status} after $sth->execute().
-<H4><A NAME="4.16.3">4.16.3</A>) Wouldn't use of currval() and nextval() lead to a race condition with other concurrent backend processes?</H4><P>
+Finally, you could use the <A HREF="#4.17"><small>OID</small></A>
+returned from the INSERT statement to look up the default value, though
+this is probably the least portable approach. In Perl, using DBI with
+Edmund Mergl's DBD::Pg module, the oid value is made available via
+<I>$sth->{pg_oid_status} after $sth->execute().</I>
+
+<H4><A NAME="4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to
+a race condition with other users?</H4><P>
-No. That has been handled by the backends.
+No. This is handled by the backends.
-<H4><A NAME="4.17">4.17</A>) What is an oid? What is a tid?</H4><P>
+<H4><A NAME="4.17">4.17</A>) What is an <small>OID</small>? What is a
+<small>TID</small>?</H4><P>
-Oids are PostgreSQL's answer to unique row ids. Every row that is
-created in PostgreSQL gets a unique oid. All oids generated during
-initdb are less than 16384 (from <I>backend/access/transam.h</I>). All
-user-created oids are equal or greater that this. By default, all these
-oids are unique not only within a table, or database, but unique within
-the entire PostgreSQL installation.<P>
+<small>OID</small>s are PostgreSQL's answer to unique row ids. Every
+row that is created in PostgreSQL gets a unique <small>OID</small>. All
+<small>OID</small>s generated during <I>initdb</I> are less than 16384
+(from <I>backend/access/transam.h</I>). All user-created
+<small>OID</small>s are equal to or greater than this. By default, all
+these <small>OID</small>s are unique not only within a table or
+database, but unique within the entire PostgreSQL installation.<P>
-PostgreSQL uses oids in its internal system tables to link rows between
-tables. These oids can be used to identify specific user rows and used
-in joins. It is recommended you use column type oid to store oid
-values. See the <I>sql(l)</I> manual page to see the other internal columns.
-
You can create an index on the oid field for faster access.<P>
+PostgreSQL uses <small>OID</small>s in its internal system tables to link rows between
+tables. These <small>OID</small>s can be used to identify specific user rows and used
+in joins. It is recommended you use column type <small>OID</small> to
+store <small>OID</small>
+
values. You can create an index on the <small>OID</small> field for faster access.<P>
-Oids are assigned to all new rows from a central area that is used by
-all databases. If you want to change the oid to something else, or if
-you want to make a copy of the table, with the original oid's, there is
+O<small>id</small>s are assigned to all new rows from a central area that is used by
+all databases. If you want to change the <small>OID</small> to something else, or if
+you want to make a copy of the table, with the original <small>OID</small>'s, there is
no reason you can't do it:
<PRE>
CREATE TABLE new_table(old_oid oid, mycol int);
- SELECT INTO new SELECT old_oid, mycol FROM old;
+ SELECT old_oid, mycol INTO new FROM old;
COPY new TO '/tmp/pgtable';
DELETE FROM new;
COPY new WITH OIDS FROM '/tmp/pgtable';
-->
</PRE><P>
-Tids are used to identify specific physical rows with block and offset
+O<small>ID</small>s are stored as 4-byte integers, and will overflow
+at 4 billion. No one has reported this ever happening, and we plan to
+have the limit removed before anyone does.<P>
+
+T<small>ID</small>s are used to identify specific physical rows with block and offset
values. Tids change after rows are modified or reloaded. They are used
by index entries to point to physical rows.<P>
-<H4><A NAME="4.18">4.18</A>) What is the meaning of some of the terms
+<H4><A NAME="4.18">4.18</A>) What is the meaning of some of the terms
used in PostgreSQL?</H4><P>
Some of the source code and older documentation use terms that have more
<LI> retrieve, select
<LI> replace, update
<LI> append, insert
-<LI> oid, serial value
+<LI> <small>OID</small>, serial value
<LI> portal, cursor
<LI> range variable, table name, table alias
</UL><P>
-<H4><A NAME="4.19">4.19</A>) Why do I get the error "FATAL: palloc
-failure: memory exhausted?"<BR></H4><P>
+A list of general database terms can be found at: <a
+href="http://www.comptechnews.com/~reaster/dbdesign.html">
+http://www.comptechnews.com/~reaster/dbdesign.html</a><P>
+
+<H4><A NAME="4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
+failure: memory exhausted?"</I><BR></H4><P>
It is possible you have run out of virtual memory on your system, or
your kernel has a low limit for certain resources. Try this before
-starting the postmaster:
+starting the <i>postmaster:</i>
<PRE>
ulimit -d 65536
</CODE> around any use of a large object handle, that is,
surrounding <CODE>lo_open</CODE> ... <CODE>lo_close.</CODE><P>
-Current PostgreSQL enforces the rule by closing large object handles at
-transaction commit, which will be instantly upon completion of the
-<I>lo_open</I> command if you are not inside a transaction. So the
-first attempt to do anything with the handle will draw <I>invalid large
-obj descriptor.</I> So code that used to work (at least most of the
-time) will now generate that error message if you fail to use a
-transaction.<P>
+Currently PostgreSQL enforces the rule by closing large object handles
+at transaction commit. So the first attempt to do anything with the
+handle will draw <I>invalid large obj descriptor.</I> So code that used
+to work (at least most of the time) will now generate that error message
+if you fail to use a transaction.<P>
If you are using a client interface like ODBC you may need to set
<CODE>auto-commit off.</CODE><P>
<H4><A NAME="4.22">4.22</A>) How do I create a column that will default to the
current time?<BR></H4><P>
-This way always works:
-<CODE><PRE>
- CREATE TABLE test (x int, modtime timestamp default now() );
-</PRE></CODE>
-In releases 7.0 and later, you may use:
+Use <i>now()</i>:
<CODE><PRE>
- create table test (x int, modtime timestamp default 'now');
+ CREATE TABLE test (x int, modtime timestamp DEFAULT now() );
</PRE></CODE>
<P>
-<H4><A NAME="4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so
-slow?<BR></H4><P>
-Currently, we join subqueries to outer queries by sequential scanning
+<H4><A NAME="4.23">4.23</A>) Why are my subqueries using
+
<CODE><small>IN</small></CODE> so slow?<BR></H4><P>
+Currently, we join subqueries to outer queries by sequentially scanning
the result of the subquery for each row of the outer query. A workaround
-is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>. For example,
-change:
+is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>:
<CODE><PRE>
SELECT *
FROM tab
</PRE></CODE>
We hope to fix this limitation in a future release.
+<H4><A NAME="4.24">4.24</A>) How do I do an <i>outer</i> join?<BR></H4><P>
+PostgreSQL does not support outer joins in the current release. They can
+be simulated using <small>UNION</small> and <small>NOT IN</small>. For
+example, when joining <i>tab1</i> and <i>tab2,</i> the following query
+does an <i>outer</i> join of the two tables:
+<PRE>
+ SELECT tab1.col1, tab2.col2
+ FROM tab1, tab2
+ WHERE tab1.col1 = tab2.col1
+ UNION ALL
+ SELECT tab1.col1, NULL
+ FROM tab1
+ WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
+ ORDER BY tab1.col1
+</PRE>
+
<HR>
<H2><CENTER>Extending PostgreSQL</CENTER></H2><P>
-<H4><A NAME="5.1">5.1</A>) I wrote a user-defined function. When
+<H4><A NAME="5.1">5.1</A>) I wrote a user-defined function. When
I run it in <I>psql,</I> why does it dump core?</H4><P>
The problem could be a number of things. Try testing your user-defined
-function in a stand alone test program first.
+function in a stand-alone test program first.
-<H4><A NAME="5.2">5.2</A>) What does the message:
-<I>
NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?</H4><P>
+<H4><A NAME="5.2">5.2</A>) What does the message
+<I>
"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?</H4><P>
-You are <I>pfree'ing</I> something that was not <I>palloc'ed.</I>
+You are <I>pfree'</I>ing something that was not <I>palloc'</I>ed.
Beware of mixing <I>malloc/free</I> and <I>palloc/pfree.</I>
-<H4><A NAME="5.3">5.3</A>) How can I contribute some nifty new types and
-functions
for PostgreSQL?</H4><P>
+<H4><A NAME="5.3">5.3</A>) How can I contribute some nifty new types and
+functions
to PostgreSQL?</H4><P>
-Send your extensions to the pgsql-hackers mailing list, and they will
+Send your extensions to the <I>pgsql-hackers</I> mailing list, and they will
eventually end up in the <I>contrib/</I> subdirectory.<P>
-<H4><A NAME="5.4">5.4</A>) How do I write a C function to return a
+<H4><A NAME="5.4">5.4</A>) How do I write a C function to return a
tuple?</H4><P>
This requires wizardry so extreme that the authors have never
tried it, though in principle it can be done.<P>
-<H4><A NAME="5.5">5.5</A>) I have changed a source file. Why does the
-recompile
does not see the change?</H4><P>
+<H4><A NAME="5.5">5.5</A>) I have changed a source file. Why does the
+recompile not see the change?</H4><P>
-The Makefiles do not have the proper dependencies for include files. You
-have to do a <I>make clean</I> and then another <I>make</I>.
- You
-have to do a <I>make clean</I> and then another <I>make.</I><P>
+The <I>Makefiles</I> do not have the proper dependencies for include files. You
+have to do a <I>make clean</I> and then another <I>make</I>.<P>
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