Horton

Re: remove spurious CREATE INDEX CONCURRENTLY wait

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Michael Paquier <michael@paquier.xyz>, Dmitry Dolgov <9erthalion6@gmail.com>, James Coleman <jtc331@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-11-11T02:07:24Z
Lists: pgsql-hackers 
Hi,

On 2020-11-25 17:03:58 -0300, Alvaro Herrera wrote:
> On 2020-Nov-23, Andres Freund wrote:
> 
> > On 2020-11-23 12:30:05 -0300, Alvaro Herrera wrote:
> 
> > > In other words, my conclusion is that there definitely is a bug here and
> > > I am going to restore the use of exclusive lock for setting the
> > > statusFlags.
> > 
> > Cool.
> 
> Here's a patch.
> 
> Note it also moves the computation of vacuum's Xmin (per
> GetTransactionSnapshot) to *after* the bit has been set in statusFlags.

> From b813c67a4abe2127b8bd13db7e920f958db15d59 Mon Sep 17 00:00:00 2001
> From: Alvaro Herrera <alvherre@alvh.no-ip.org>
> Date: Tue, 24 Nov 2020 18:10:42 -0300
> Subject: [PATCH] Restore lock level to update statusFlags
> 
> Reverts 27838981be9d (some comments are kept).  Per discussion, it does
> not seem safe to relax the lock level used for this; in order for it to
> be safe, there would have to be memory barriers between the point we set
> the flag and the point we set the trasaction Xid, which perhaps would
> not be so bad; but there would also have to be barriers at the readers'
> side, which from a performance perspective might be bad.
> 
> Now maybe this analysis is wrong and it *is* safe for some reason, but
> proof of that is not trivial.

I just noticed that this commit (dcfff74fb16) didn't revert the change of lock
level in ReplicationSlotRelease(). Was that intentional?

Greetings,

Andres Freund

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