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Re: logical decoding - GetOldestXmin

Michael Paquier <michael.paquier@gmail.com>

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From: Michael Paquier <michael.paquier@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@2ndquadrant.com>, Peter Geoghegan <peter@2ndquadrant.com>, pgsql-hackers@postgresql.org
Date: 2012-12-14T03:40:36Z
Lists: pgsql-hackers 
On Fri, Dec 14, 2012 at 2:29 AM, Robert Haas <robertmhaas@gmail.com> wrote:

> On Thu, Dec 13, 2012 at 3:03 PM, Andres Freund <andres@2ndquadrant.com>
> wrote:
> > It moves a computation of the sort of:
> >
> > result -= vacuum_defer_cleanup_age;
> > if (!TransactionIdIsNormal(result))
> >    result = FirstNormalTransactionId;
> >
> > inside ProcArrayLock. But I can't really imagine that to be relevant...
>
> I can.  Go look at some of the 9.2 optimizations around
> GetSnapshotData().  Those made a BIG difference under heavy
> concurrency and they were definitely micro-optimization.  For example,
> the introduction of NormalTransactionIdPrecedes() was shockingly
> effective.
>

The two commits coming to my mind are:
- ed0b409 (Separate PGPROC into PGPROC and PGXACT)
- 0d76b60 (introduction of NormalTransactionIdPrecedes)
Those ones really improved concurrency performance.
-- 
Michael Paquier
http://michael.otacoo.com

Commits

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

  1. Background worker processes

  2. Rearrange storage of data in xl_running_xacts.

  3. Basic binary heap implementation.

  4. Embedded list interface

  5. Refactor xlog.c to create src/backend/postmaster/startup.c