Horton

Re: prevent immature WAL streaming

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: "alvherre@alvh.no-ip.org" <alvherre@alvh.no-ip.org>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, "mengjuan.cmj@alibaba-inc.com" <mengjuan.cmj@alibaba-inc.com>, "Jakub.Wartak@tomtom.com" <Jakub.Wartak@tomtom.com>
Date: 2021-08-25T12:32:31Z
Lists: pgsql-hackers 
On 2021-Aug-24, Bossart, Nathan wrote:

> If moving RegisterSegmentBoundary() is sufficient to prevent the flush
> pointer from advancing before we register the boundary, I bet we could
> also remove the WAL writer nudge.

Can you elaborate on this?  I'm not sure I see the connection.

> Another interesting thing I see is that the boundary stored in
> earliestSegBoundary is not necessarily the earliest one.  It's just
> the first one that has been registered.  I did this for simplicity for
> the .ready file fix, but I can see it causing problems here.

Hmm, is there really a problem here?  Surely the flush point cannot go
past whatever has been written.  If somebody is writing an earlier
section of WAL, then we cannot move the flush pointer to a later
position.  So it doesn't matter if the earliest point we have registered
is the true earliest -- we only care for it to be the earliest that is
past the flush point.

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/

Commits

  1. Fix determination of broken LSN in OVERWRITTEN_CONTRECORD

  2. Fix instability in 026_overwrite_contrecord.pl test.

  3. Fix typo

  4. Change recently added test code for stability

  5. Remove unstable, unnecessary test; fix typo

  6. Repair two portability oversights of new test

  7. Fix WAL replay in presence of an incomplete record

  8. Document XLOG_INCLUDE_XID a little better

  9. Revert "Avoid creating archive status ".ready" files too early"

  10. Avoid creating archive status ".ready" files too early

  11. Fix scenario where streaming standby gets stuck at a continuation record.

  12. Teach xlogreader to follow timeline switches

  13. Forbid using pg_xlogfile_name() and pg_xlogfile_name_offset() during