Horton

Re: remove spurious CREATE INDEX CONCURRENTLY wait

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, James Coleman <jtc331@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-11-10T01:39:57Z
Lists: pgsql-hackers 
On Mon, Nov 09, 2020 at 08:32:13PM -0500, Tom Lane wrote:
> Do we really need exclusive lock on the ProcArray to make this flag
> change?  That seems pretty bad from a concurrency standpoint.

Any place where we update vacuumFlags acquires an exclusive LWLock on
ProcArrayLock.  That's held for a very short time, so IMO it won't
matter much in practice, particularly if you compare that with the
potential gains related to the existing wait phases.
--
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