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Improve TimestampDifferenceMilliseconds to cope with overflow sanely.

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We'd like to use TimestampDifferenceMilliseconds with the stop_time
possibly being TIMESTAMP_INFINITY, but up to now it's disclaimed
responsibility for overflow cases.  Define it to clamp its output to
the range [0, INT_MAX], handling overflow correctly.  (INT_MAX rather
than LONG_MAX seems appropriate, because the function is already
described as being intended for calculating wait times for WaitLatch
et al, and that infrastructure only handles waits up to INT_MAX.
Also, this choice gets rid of cross-platform behavioral differences.)

Having done that, we can replace some ad-hoc code in walreceiver.c
with a simple call to TimestampDifferenceMilliseconds.

While at it, fix some buglets in existing callers of
TimestampDifferenceMilliseconds: basebackup_copy.c had not read the
memo about TimestampDifferenceMilliseconds never returning a negative
value, and postmaster.c had not read the memo about Min() and Max()
being macros with multiple-evaluation hazards.  Neither of these
quite seem worth back-patching.

Patch by me; thanks to Nathan Bossart for review.

Discussion: https://postgr.es/m/3126727.1674759248@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2023-01-26 17:09:12 -05:00
parent 24ff700f6a
commit 3a28d78089
4 changed files with 24 additions and 23 deletions
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3
src/backend/backup/basebackup_copy.c
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@@ -215,7 +215,8 @@ bbsink_copystream_archive_contents(bbsink *sink, size_t len)
* the system clock was set backward, so that such occurrences don't
* have the effect of suppressing further progress messages.
*/
if (ms < 0 || ms >= PROGRESS_REPORT_MILLISECOND_THRESHOLD)
if (ms >= PROGRESS_REPORT_MILLISECOND_THRESHOLD ||
now < mysink->last_progress_report_time)
{
mysink->last_progress_report_time = now;