Fix performance bug in write_syslog(): the code to preferentially break the

log message at newlines cost O(N^2) for very long messages with few or no
newlines.  For messages in the megabyte range this became the dominant cost.
Per gripe from Achilleas Mantzios.

Patch all the way back, since this is a safe change with no portability
risks.  I am also thinking of increasing PG_SYSLOG_LIMIT, but that should
be done separately.

diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index d21ca068b0b92d2ae84e87767c576aeb5e82dfdf..0d4fd56a2242c5de73199cf86de86a18604ed85b 100644 (file)
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -42,7 +42,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/utils/error/elog.c,v 1.203 2008/03/24 18:08:47 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/utils/error/elog.c,v 1.204 2008/07/08 22:17:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1306,6 +1306,7 @@ write_syslog(int level, const char *line)
    static unsigned long seq = 0;
 
    int         len;
+   const char *nlpos;
 
    /* Open syslog connection if not done yet */
    if (!openlog_done)
@@ -1328,17 +1329,17 @@ write_syslog(int level, const char *line)
     * fact, it does work around by splitting up messages into smaller pieces.
     *
     * We divide into multiple syslog() calls if message is too long or if the
-    * message contains embedded NewLine(s) '\n'.
+    * message contains embedded newline(s).
     */
    len = strlen(line);
-   if (len > PG_SYSLOG_LIMIT || strchr(line, '\n') != NULL)
+   nlpos = strchr(line, '\n');
+   if (len > PG_SYSLOG_LIMIT || nlpos != NULL)
    {
        int         chunk_nr = 0;
 
        while (len > 0)
        {
            char        buf[PG_SYSLOG_LIMIT + 1];
-           const char *nlpos;
            int         buflen;
            int         i;
 
@@ -1347,11 +1348,12 @@ write_syslog(int level, const char *line)
            {
                line++;
                len--;
+               /* we need to recompute the next newline's position, too */
+               nlpos = strchr(line, '\n');
                continue;
            }
 
            /* copy one line, or as much as will fit, to buf */
-           nlpos = strchr(line, '\n');
            if (nlpos != NULL)
                buflen = nlpos - line;
            else