Horton

Re: LogwrtResult contended spinlock

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@lists.postgresql.org, Jaime Casanova <jaime.casanova@2ndquadrant.com>
Date: 2021-11-22T21:56:43Z
Lists: pgsql-hackers

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There was an earlier comment by Andres that asyncXactLSN should also be
atomic, to avoid an ugly spinlock interaction with the new atomic-based
logwrtResult.  The 0002 here is an attempt at doing that; I found that
it also needed to change WalWriterSleeping to use atomics, to avoid
XLogSetAsyncXactLSN having to grab the spinlock for that.


-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/
"Learn about compilers. Then everything looks like either a compiler or
a database, and now you have two problems but one of them is fun."
            https://twitter.com/thingskatedid/status/1456027786158776329

Commits

  1. Remove bogus assertion in pg_atomic_monotonic_advance_u64

  2. Add XLogCtl->logInsertResult

  3. Operate XLogCtl->log{Write,Flush}Result with atomics

  4. Split XLogCtl->LogwrtResult into separate struct members

  5. Introduce atomic read/write functions with full barrier semantics.

  6. Reduce the number of GetFlushRecPtr() calls done by walsenders.

  7. Remove most volatile qualifiers from xlog.c