Re: Do not fail WAL buffers read after on-disk xlog removal

Hi Kirill,

The fix looks right to me. Your test fails 10 of 10 runs on master
and passes 10 of 10 with the fix.

A new walsender still fails, because its reader starts with
seg.ws_tli = 0, so the first read never uses the buffers. If I
terminate the paused walsender in your test, the receiver never
catches up, with or without the fix. Passing sendTimeLine fixes it
for me when wal_buffers is larger than a segment. Test and change
attached.

Also, the pg_stat_io check passes without the fix too, so I would drop
it. And since 16 never read from the buffers, I would keep this to
master.

Thanks,
Shihao