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 8a3677a3c096548c1192bad5e21d3e456696d68c..f973f5a529effd133eb9a5b1c4acac2666607ec0 100644 (file)
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -1199,6 +1199,7 @@ 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)
@@ -1221,10 +1222,11 @@ 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;
 
@@ -1239,15 +1241,19 @@ write_syslog(int level, const char *line)
                        {
                                line++;
                                len--;
+                               /* we need to recompute the next newline's position, too */
+                               nlpos = strchr(line, '\n');
                                continue;
                        }
 
-                       strncpy(buf, line, PG_SYSLOG_LIMIT);
-                       buf[PG_SYSLOG_LIMIT] = '\0';
-                       if (strchr(buf, '\n') != NULL)
-                               *strchr(buf, '\n') = '\0';
-
-                       buflen = strlen(buf);
+                       /* copy one line, or as much as will fit, to buf */
+                       if (nlpos != NULL)
+                               buflen = nlpos - line;
+                       else
+                               buflen = len;
+                       buflen = Min(buflen, PG_SYSLOG_LIMIT);
+                       memcpy(buf, line, buflen);
+                       buf[buflen] = '\0';
 
                        /* trim to multibyte letter boundary */
                        buflen = pg_mbcliplen(buf, buflen, buflen);