Re: Proposal of tunable fix for scalability of 8.4 - Mailing list pgsql-performance

From Simon Riggs
Subject Re: Proposal of tunable fix for scalability of 8.4
Date
Msg-id 1237362833.3953.186.camel@ebony.2ndQuadrant
Whole thread Raw
In response to Re: Proposal of tunable fix for scalability of 8.4  (Matthew Wakeling <matthew@flymine.org>)
Responses Re: Proposal of tunable fix for scalability of 8.4  (Matthew Wakeling <matthew@flymine.org>)
Re: Proposal of tunable fix for scalability of 8.4  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: Proposal of tunable fix for scalability of 8.4  (Scott Carey <scott@richrelevance.com>)
List pgsql-performance
On Mon, 2009-03-16 at 16:26 +0000, Matthew Wakeling wrote:
> One possibility would be for the locks to alternate between exclusive
> and
> shared - that is:
>
> 1. Take a snapshot of all shared waits, and grant them all -
> thundering
>      herd style.
> 2. Wait until ALL of them have finished, granting no more.
> 3. Take a snapshot of all exclusive waits, and grant them all, one by
> one.
> 4. Wait until all of them have been finished, granting no more.
> 5. Back to (1)

I agree with that, apart from the "granting no more" bit.

Currently we queue up exclusive locks, but there is no need to since for
ProcArrayLock commits are all changing different data.

The most useful behaviour is just to have two modes:
* exclusive-lock held - all other x locks welcome, s locks queue
* shared-lock held - all other s locks welcome, x locks queue

This *only* works for ProcArrayLock.

--
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support


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