Implement rate-limiting logic on how often backends will attempt to send

messages to the stats collector.  This avoids the problem that enabling
stats_row_level for autovacuum has a significant overhead for short
read-only transactions, as noted by Arjen van der Meijden.  We can avoid
an extra gettimeofday call by piggybacking on the one done for WAL-logging
xact commit or abort (although that doesn't help read-only transactions,
since they don't WAL-log anything).

In my proposal for this, I noted that we could change the WAL log entries
for commit/abort to record full TimestampTz precision, instead of only
time_t as at present.  That's not done in this patch, but will be committed
separately.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/include/utils/timestamp.h b/src/include/utils/timestamp.h
index 0d31cc02940..594cd61e884 100644
--- a/src/include/utils/timestamp.h
+++ b/src/include/utils/timestamp.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/timestamp.h,v 1.67 2007/02/16 03:39:45 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/utils/timestamp.h,v 1.68 2007/04/30 03:23:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -311,6 +311,9 @@ extern TimestampTz GetCurrentTimestamp(void);
 
 extern void TimestampDifference(TimestampTz start_time, TimestampTz stop_time,
 					long *secs, int *microsecs);
+extern bool TimestampDifferenceExceeds(TimestampTz start_time,
+									   TimestampTz stop_time,
+									   int msec);
 
 extern TimestampTz time_t_to_timestamptz(time_t tm);
 extern time_t timestamptz_to_time_t(TimestampTz t);