Re: Implement waiting for wal lsn replay: reloaded

I wrote:
> 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.

I'm wrong: there's only one culprit.  The other big change in runtime
today is that src/test/recovery's t/033_replay_tsp_drops.pl went from
about 4 seconds to about 46, and that jump also happened at 7e8aeb9e4.
So we still have a mystery, but it's "what do those two tests have in
common that is shared by no others?".

            regards, tom lane