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Re: Synchronized Scan benchmark results

From: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
To: "Jeff Davis" <pgsql(at)j-davis(dot)com>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Synchronized Scan benchmark results
Date: 2007-04-03 09:01:39
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Mon, 2007-04-02 at 16:14 -0700, Jeff Davis wrote:

> The results are very positive and quite conclusive.

Can we show some summary results?

I'm happy that the scans stay together all the way around, even handling
the max-> 0 blockid transition well. So definite winner for me.

> However, the "sync_seqscan_offset" aspect of my patch, which attempts to
> use pages that were cached before the scan began, did not show a lot of
> promise. That aspect of my patch may end up being cut.

Yes, please remove :-)

> The primary aspect of my patch, the Synchronized Scanning, performed
> great though. Even the CFQ scheduler, that does not appear to properly
> read ahead, performed substantially better than plain 8.2.3. And even
> better, Simon's patch didn't seem to hurt Synchronized Scans at all.
> Out of the 36 runs I did, a couple appear anomalous. I will retest those
> soon.

Which ones were they?

> Note: I posted the versions of the patches that I used for the tests on
> the page above. The version of Simon's patch that I used did not apply
> cleanly to 8.2.3, but the only problem appeared to be in copy.c, so I
> went ahead with the tests. If this somehow compromised the patch, then
> let me know.

[It was never designed to apply cleanly to 8.2.3, as we might guess]
That was v2, the current v3 should be OK because I removed the
experimental COPY interaction. That will not have affected the tests.

I would like to see some tests with different queries that have varying
I/O and CPU requirements to see if they stay together too. That won't
block the patch, but it will help everybody understand what the range of
real world applicability there is in this. I'd guess this can benefit us
sufficiently frequently in most cases that its worth it.

  Simon Riggs             

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