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, 2 insertions, 7 deletions

diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index a55d28fec34..1f49402d1f4 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -1196,20 +1196,15 @@ pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result)
 			{
 				int			wc;
 				TimestampTz now = GetCurrentTimestamp();
-				long		secs;
-				int			microsecs;
 				long		cur_timeout;
 
 				/* If timeout has expired, give up, else get sleep time. */
-				if (now >= endtime)
+				cur_timeout = TimestampDifferenceMilliseconds(now, endtime);
+				if (cur_timeout <= 0)
 				{
 					timed_out = true;
 					goto exit;
 				}
-				TimestampDifference(now, endtime, &secs, &microsecs);
-
-				/* To protect against clock skew, limit sleep to one minute. */
-				cur_timeout = Min(60000, secs * USECS_PER_SEC + microsecs);
 
 				/* Sleep until there's something to do */
 				wc = WaitLatchOrSocket(MyLatch,