Horton

Re: LogwrtResult contended spinlock

Alvaro Herrera <alvherre@alvh.no-ip.org>

View thread View on postgr.es
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>, pgsql-hackers@lists.postgresql.org, Jaime Casanova <jcasanov@systemguards.com.ec>
Date: 2022-03-22T16:11:20Z
Lists: pgsql-hackers

Attachments

On 2022-Mar-22, Tom Lane wrote:

> I looked briefly at 0001, and I've got to say that I disagree with
> your decision to rearrange the representation of the local LogwrtResult
> copy.  It clutters the patch tremendously and makes it hard to
> understand what the actual functional change is.  Moreover, I'm
> not entirely convinced that it's a notational improvement in the
> first place.
> 
> Perhaps it'd help if you split 0001 into two steps, one to do the
> mechanical change of the representation and then a second patch that
> converts the shared variable to atomics.  Since you've moved around
> the places that read the shared variable, that part is subtler than
> one could wish and really needs to be studied on its own.

Hmm, I did it the other way around: first change to use atomics, then
the mechanical change.  I think that makes the usefulness of the change
more visible, because before the atomics use the use of the combined
struct as a unit remains sensible.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
Officer Krupke, what are we to do?
Gee, officer Krupke, Krup you! (West Side Story, "Gee, Officer Krupke")

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