| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Neil Conway <neilc(at)samurai(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, pgsql-hackers(at)postgreSQL(dot)org |
| Subject: | Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable |
| Date: | 2008-01-28 23:51:54 |
| Message-ID: | 1201564314.4257.815.camel@ebony.site |
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| Lists: | pgsql-hackers pgsql-patches |
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
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