Fix and simplify some usages of TimestampDifference().

Introduce TimestampDifferenceMilliseconds() to simplify callers
that would rather have the difference in milliseconds, instead of
the select()-oriented seconds-and-microseconds format.  This gets
rid of at least one integer division per call, and it eliminates
some apparently-easy-to-mess-up arithmetic.

Two of these call sites were in fact wrong:

* pg_prewarm's autoprewarm_main() forgot to multiply the seconds
by 1000, thus ending up with a delay 1000X shorter than intended.
That doesn't quite make it a busy-wait, but close.

* postgres_fdw's pgfdw_get_cleanup_result() thought it needed to compute
microseconds not milliseconds, thus ending up with a delay 1000X longer
than intended.  Somebody along the way had noticed this problem but
misdiagnosed the cause, and imposed an ad-hoc 60-second limit rather
than fixing the units.  This was relatively harmless in context, because
we don't care that much about exactly how long this delay is; still,
it's wrong.

There are a few more callers of TimestampDifference() that don't
have a direct need for seconds-and-microseconds, but can't use
TimestampDifferenceMilliseconds() either because they do need
microsecond precision or because they might possibly deal with
intervals long enough to overflow 32-bit milliseconds.  It might be
worth inventing another API to improve that, but that seems outside
the scope of this patch; so those callers are untouched here.

Given the fact that we are fixing some bugs, and the likelihood
that future patches might want to back-patch code that uses this
new API, back-patch to all supported branches.

Alexey Kondratov and Tom Lane

Discussion: https://postgr.es/m/3b1c053a21c07c1ed5e00be3b2b855ef@postgrespro.ru

1 files changed, 1 insertions, 7 deletions

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index dc4b86ba683..86e6f4e433b 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -2079,8 +2079,6 @@ WalSndComputeSleeptime(TimestampTz now)
 	if (wal_sender_timeout > 0 && last_reply_timestamp > 0)
 	{
 		TimestampTz wakeup_time;
-		long		sec_to_timeout;
-		int			microsec_to_timeout;
 
 		/*
 		 * At the latest stop sleeping once wal_sender_timeout has been
@@ -2099,11 +2097,7 @@ WalSndComputeSleeptime(TimestampTz now)
 													  wal_sender_timeout / 2);
 
 		/* Compute relative time until wakeup. */
-		TimestampDifference(now, wakeup_time,
-							&sec_to_timeout, &microsec_to_timeout);
-
-		sleeptime = sec_to_timeout * 1000 +
-			microsec_to_timeout / 1000;
+		sleeptime = TimestampDifferenceMilliseconds(now, wakeup_time);
 	}
 
 	return sleeptime;