Back-patch fix for 'Sorcerer's Apprentice' syndrome wherein md.c would

create a vast quantity of zero-length files if asked to access a block
number far beyond the actual end of a relation.

diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index e4fd3120d2ca74518421425a2e1409460c70ab21..9824cb35c5cbfe743410601f2ae956a43c6b003c 100644 (file)
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.68 2000/05/25 23:30:20 tgl Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.68.2.1 2000/09/23 22:11:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -130,6 +130,7 @@ mdcreate(Relation reln)
    char       *path;
 
    Assert(reln->rd_unlinked && reln->rd_fd < 0);
+
    path = relpath(RelationGetPhysicalRelationName(reln));
 #ifndef __CYGWIN32__
    fd = FileNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL, 0600);
@@ -138,19 +139,21 @@ mdcreate(Relation reln)
 #endif
 
    /*
-    * During bootstrap processing, we skip that check, because pg_time,
-    * pg_variable, and pg_log get created before their .bki file entries
-    * are processed.
-    *
-    * For cataloged relations,pg_class is guaranteed to have an unique
+    * For cataloged relations, pg_class is guaranteed to have a unique
     * record with the same relname by the unique index. So we are able to
-    * reuse existent files for new catloged relations. Currently we reuse
+    * reuse existent files for new cataloged relations. Currently we reuse
     * them in the following cases. 1. they are empty. 2. they are used
     * for Index relations and their size == BLCKSZ * 2.
+    *
+    * During bootstrap processing, we skip that check, because pg_time,
+    * pg_variable, and pg_log get created before their .bki file entries
+    * are processed.
     */
 
    if (fd < 0)
    {
+       int     save_errno = errno;
+
        if (!IsBootstrapProcessingMode() &&
            reln->rd_rel->relkind == RELKIND_UNCATALOGED)
            return -1;
@@ -161,11 +164,15 @@ mdcreate(Relation reln)
        fd = FileNameOpenFile(path, O_RDWR | O_BINARY, 0600);
 #endif
        if (fd < 0)
+       {
+           /* be sure to return the error reported by create, not open */
+           errno = save_errno;
            return -1;
+       }
        if (!IsBootstrapProcessingMode())
        {
            bool        reuse = false;
-           int         len = FileSeek(fd, 0L, SEEK_END);
+           long        len = FileSeek(fd, 0L, SEEK_END);
 
            if (len == 0)
                reuse = true;
@@ -175,9 +182,12 @@ mdcreate(Relation reln)
            if (!reuse)
            {
                FileClose(fd);
+               /* be sure to return the error reported by create */
+               errno = save_errno;
                return -1;
            }
        }
+       errno = 0;
    }
    reln->rd_unlinked = false;
 
@@ -733,9 +743,16 @@ mdnblocks(Relation reln)
 
            if (v->mdfd_chain == (MdfdVec *) NULL)
            {
+               /*
+                * Because we pass O_CREAT, we will create the next segment
+                * (with zero length) immediately, if the last segment is of
+                * length REL_SEGSIZE.  This is unnecessary but harmless, and
+                * testing for the case would take more cycles than it seems
+                * worth.
+                */
                v->mdfd_chain = _mdfd_openseg(reln, segno, O_CREAT);
                if (v->mdfd_chain == (MdfdVec *) NULL)
-                   elog(ERROR, "cannot count blocks for %s -- open failed",
+                   elog(ERROR, "cannot count blocks for %s -- open failed: %m",
                         RelationGetRelationName(reln));
            }
 
@@ -1075,11 +1092,20 @@ _mdfd_getseg(Relation reln, int blkno)
 
        if (v->mdfd_chain == (MdfdVec *) NULL)
        {
-           v->mdfd_chain = _mdfd_openseg(reln, i, O_CREAT);
+           /*
+            * We will create the next segment only if the target block
+            * is within it.  This prevents Sorcerer's Apprentice syndrome
+            * if a bug at higher levels causes us to be handed a ridiculously
+            * large blkno --- otherwise we could create many thousands of
+            * empty segment files before reaching the "target" block.  We
+            * should never need to create more than one new segment per call,
+            * so this restriction seems reasonable.
+            */
+           v->mdfd_chain = _mdfd_openseg(reln, i, (segno == 1) ? O_CREAT : 0);
 
            if (v->mdfd_chain == (MdfdVec *) NULL)
-               elog(ERROR, "cannot open segment %d of relation %s",
-                    i, RelationGetRelationName(reln));
+               elog(ERROR, "cannot open segment %d of relation %s (target block %d): %m",
+                    i, RelationGetRelationName(reln), blkno);
        }
        v = v->mdfd_chain;
    }
@@ -1097,8 +1123,10 @@ _mdfd_getseg(Relation reln, int blkno)
  * "blind" with no Relation struct.  We assume that we are not likely to
  * touch the same relation again soon, so we do not create an FD entry for
  * the relation --- we just open a kernel file descriptor which will be
- * used and promptly closed.  The return value is the kernel descriptor,
- * or -1 on failure.
+ * used and promptly closed.  We also assume that the target block already
+ * exists, ie, we need not extend the relation.
+ *
+ * The return value is the kernel descriptor, or -1 on failure.
  */
 
 static int