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@2ndquadrant.com>
Cc: James Coleman <jtc331@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-08-20T06:11:19Z
Lists: pgsql-hackers 
On Wed, Aug 19, 2020 at 02:16:46PM -0400, Alvaro Herrera wrote:
> I did not set the flag in REINDEX CONCURRENTLY, but as I understand it
> can be done too, since in essence it's the same thing as a CIC from a
> snapshot management point of view.

Yes, I see no problems for REINDEX CONCURRENTLY as well as long as
there are no predicates and expressions involved.  The transactions
that should be patched are all started in ReindexRelationConcurrently.
The transaction of index_concurrently_swap() cannot set up that
though.  Only thing to be careful is to make sure that safe_flag is
correct depending on the list of indexes worked on.

> Also, per [1], ISTM this flag could be used to tell lazy VACUUM to
> ignore the Xmin of this process too, which the previous formulation
> (where all CICs were so marked) could not.  This patch doesn't do that
> yet, but it seems the natural next step to take.
> 
> [1] https://postgr.es/m/20191101203310.GA12239@alvherre.pgsql

Could we consider renaming vacuumFlags?  With more flags associated to
a PGPROC entry that are not related to vacuum, the current naming
makes things confusing.  Something like statusFlags could fit better
in the picture?
--
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