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Re: Sync Scan update

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org, Luke Lonergan <llonergan(at)greenplum(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>
Subject: Re: Sync Scan update
Date: 2007-02-02 23:05:47
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Thread added to TODO for item:

* Allow sequential scans to take advantage of other concurrent
  sequential scans, also called "Synchronised Scanning"


Jeff Davis wrote:
> I have updated my Synchronized Scan patch and have had more time for
> testing.
> Go to
> where you can download the patch, and see the benchmarks that I've run.
> The results are very promising. I did not see any significant slowdown
> for non-concurrent scans or for scans that fit into memory, although I
> do need more testing in this area.
> The benchmarks that I ran tested the concurrent performance, and the
> results were excellent.
> I also added two new simple features to the patch (they're just
> #define'd tunables in heapam.h):
> (1) If the table is smaller than
> effective_cache_size*SYNC_SCAN_THRESHOLD then the patch doesn't do
> anything different from current behavior.
> (2) The scans can start earlier than the hint implies by setting
> SYNC_SCAN_START_OFFSET between 0 and 1. This is helpful because it makes
> the scan start in a place where the cache trail is likely to be
> continuous between the starting point and the location of an existing scan.
> I'd like any feedback, particularly any results that show a slowdown
> from current behavior. I think I fixed Luke's problem (actually, it was
> a fluke that it was even working at all), but I haven't heard back. Some
> new feedback would be very helpful.
> Thanks.
> Regards,
> 	Jeff Davis
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Have you searched our list archives?

  Bruce Momjian   bruce(at)momjian(dot)us

  + If your life is a hard drive, Christ can be your backup. +

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