Horton

Re: LogwrtResult contended spinlock

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>, Andres Freund <andres@anarazel.de>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Jaime Casanova <jaime.casanova@2ndquadrant.com>
Date: 2021-01-22T13:23:46Z
Lists: pgsql-hackers 
Hi Alvaro,

On Wed, Nov 25, 2020 at 12:02 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2020-Nov-24, Anastasia Lubennikova wrote:
>
> > On 04.09.2020 20:13, Andres Freund wrote:
>
> > > Re general routine: On second thought, it might actually be worth having
> > > it. Even just for LSNs - there's plenty places where it's useful to
> > > ensure a variable is at least a certain size.  I think I would be in
> > > favor of a general helper function.
> > Do you mean by general helper function something like this?
> >
> > void
> > swap_lsn(XLogRecPtr old_value, XLogRecPtr new_value, bool to_largest)
>
> Something like that, yeah, though maybe name it "pg_atomic_increase_lsn"
> or some similar name that makes it clear that
>
> 1. it is supposed to use atomics
> 2. it can only be used to *advance* a value rather than a generic swap.
>
> (I'm not 100% clear that that's the exact API we need.)
>
> > This CF entry was inactive for a while. Alvaro, are you going to continue
> > working on it?
>
> Yes, please move it forward.  I'll post an update sometime before the
> next CF.

Anything update on this?

Regards,

-- 
Masahiko Sawada
EDB:  https://www.enterprisedb.com/

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