Horton

Re: foreign key locks, 2nd attempt

Alvaro Herrera <alvherre@commandprompt.com>

View thread
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Noah Misch <noah@leadboat.com>, Tom Lane <tgl@sss.pgh.pa.us>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2012-03-15T21:54:32Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Try to avoid running with a full fsync request queue.

Excerpts from Simon Riggs's message of jue mar 15 18:38:53 -0300 2012:
> On Thu, Mar 15, 2012 at 2:26 AM, Robert Haas <robertmhaas@gmail.com> wrote:

> > But that would only make sense if
> > we thought that getting rid of the fsyncs would be more valuable than
> > avoiding the blocking here, and I don't.
> 
> You're right that the existing code could use some optimisation.
> 
> I'm a little tired, but I can't see a reason to fsync this except at checkpoint.

Hang on.  What fsyncs are we talking about?  I don't see that the
multixact code calls any fsync except that checkpoint and shutdown.

> Also seeing that we issue 2 WAL records for each RI check. We issue
> one during MultiXactIdCreate/MultiXactIdExpand and then immediately
> afterwards issue a XLOG_HEAP_LOCK record. The comments on both show
> that each thinks it is doing it for the same reason and is the only
> place its being done. Alvaro, any ideas why that is.

AFAIR the XLOG_HEAP_LOCK log entry only records the fact that the row is
being locked by a multixact -- it doesn't record the contents (member
xids) of said multixact, which is what the other log entry records.

-- 
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support