Skip site navigation (1) Skip section navigation (2)

Re: Proposed patch: synchronized_scanning GUC variable

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-patches(at)postgreSQL(dot)org
Subject: Re: Proposed patch: synchronized_scanning GUC variable
Date: 2008-01-28 22:58:13
Message-ID: 1201561093.10057.655.camel@dogma.ljc.laika.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
On Sun, 2008-01-27 at 15:07 -0500, Tom Lane wrote:
> Per today's -hackers discussion, add a GUC variable to allow clients to
> disable the new synchronized-scanning behavior, and make pg_dump disable
> sync scans so that it will reliably preserve row ordering.  This is a
> pretty trivial patch, but seeing how late we are in the 8.3 release
> cycle, I thought I'd better post it for comment anyway.

I apologize for the late reply, but I have one comment I'd like to add.

> + 	if (g_fout->remoteVersion >= 80300)
> + 		do_sql_command(g_conn, "SET synchronized_scanning TO off");
> + 
> + 	/*
>   	 * Start serializable transaction to dump consistent data.
>   	 */

I think that pg_dump is a reasonable use case for synchoronized scans
when the table has not been clustered. It could potentially make pg_dump
have much less of a performance impact when run against an active
system.

I think it's worth considering enabling sync scans for non-clustered
tables if it would not interfere with the release. Of course, a painless
8.3 release is the top priority.

Regards,
	Jeff Davis


In response to

Responses

pgsql-hackers by date

Next:From: Heikki LinnakangasDate: 2008-01-28 23:13:18
Subject: Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable
Previous:From: Jeff DavisDate: 2008-01-28 22:44:52
Subject: Re: CLUSTER and synchronized scans and pg_dump et al

pgsql-patches by date

Next:From: Heikki LinnakangasDate: 2008-01-28 23:13:18
Subject: Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable
Previous:From: Simon RiggsDate: 2008-01-28 22:39:41
Subject: Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group