Re: Implement waiting for wal lsn replay: reloaded

Alexander Korotkov <aekorotkov@gmail.com> writes:
> Thank you, I've pushed your version of patchset.  I made two minor
> corrections for patch #2: mention default mode value in the header
> comment, and fallback to polling on has_wal_read_bug sparc64+ext4 bug.

I wondered why my buildfarm animals got noticeably slower today.
There seem to be a couple of culprits, but one of them is that
7e8aeb9e4 (Use WAIT FOR LSN) has caused the runtime of pg_rewind's
t/003_extrafiles.pl to go through the roof.  On indri's host, that
TAP test took about 3 seconds immediately before that commit, and
about 45 seconds immediately after.  (For scale, the core regression
tests take about 10 seconds on this machine.)  I see roughly
comparable slowdowns on other machines too.

I have not dug into why, nor do I understand why it seems like
only this one test is affected.  In any case, surely this is
unacceptable.

            regards, tom lane