Horton

Re: remove spurious CREATE INDEX CONCURRENTLY wait

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Dmitry Dolgov <9erthalion6@gmail.com>, James Coleman <jtc331@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-11-10T02:44:23Z
Lists: pgsql-hackers 
On Mon, Nov 09, 2020 at 11:31:15PM -0300, Alvaro Herrera wrote:
> Yeah ... it would be much better if we can make it use atomics instead.
> Currently it's an uint8, and in PGPROC itself it's probably not a big
> deal to enlarge that, but I fear that quadrupling the size of the
> mirroring array in PROC_HDR might be bad for performance.  However,
> maybe if we use atomics to access it, then we don't need to mirror it
> anymore?  That would need some benchmarking of GetSnapshotData.

Hmm.  If you worry about the performance impact here, it is possible
to do a small performance test without this patch.  vacuum_rel() sets
the flag for a non-full VACUUM, so with one backend running a manual
VACUUM in loop on an empty relation could apply some pressure on any
benchmark, even a simple pgbench.
--
Michael

Commits

  1. Restore lock level to set vacuum flags

  2. Restore lock level to update statusFlags

  3. Avoid spurious waits in concurrent indexing

  4. Centralize logic for skipping useless ereport/elog calls.

  5. Don't hold ProcArrayLock longer than needed in rare cases

  6. Relax lock level for setting PGPROC->statusFlags

  7. Rename PGPROC->vacuumFlags to statusFlags

  8. snapshot scalability: Move PGXACT->vacuumFlags to ProcGlobal->vacuumFlags.

  9. Allow an autovacuum worker to be interrupted automatically when it is found