Horton

Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable

Simon Riggs <simon@2ndquadrant.com>

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From: Simon Riggs <simon@2ndquadrant.com>
To: Heikki Linnakangas <heikki@enterprisedb.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Neil Conway <neilc@samurai.com>, Gregory Stark <stark@enterprisedb.com>, "Jonah H. Harris" <jonah.harris@gmail.com>, pgsql-hackers@postgreSQL.org
Date: 2008-01-28T23:51:54Z
Lists: pgsql-hackers 
On Mon, 2008-01-28 at 23:13 +0000, Heikki Linnakangas wrote:
> Tables that are seq scanned are typically very small, like a summary 
> table with just a few rows, or huge tables in a data warehousing 
> system. Between the extremes, I don't think the threshold actually has
> a very big impact.

And if you have a partitioned table with partitions inconveniently
sized? You'd need to *reduce* shared_buffers specifically to get synch
scans and BAS to kick in. Or increase partition size. Both of which
reduce the impact of the benefits we've added.

I don't think the argument that "a table is smaller than shared buffers
therefore it is already in shared buffers" holds true in all cases. I/O
does matter.

-- 
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com