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Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable

From: Euler Taveira de Oliveira <euler(at)timbira(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, 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: 2008-01-29 13:31:01
Message-ID: 479F2A95.8040700@timbira.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Simon Riggs wrote:

> 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.
> 
+1. If we go with 'enable_sync_seqcans' for 8.3, and in a future release 
cycle we do test the cases Simon described above and we agree we need to 
do a fine tune to benefit from this feature, we will need to deprecate 
'enable_sync_seqscans' and invent another one (sync_seqscans_threshold). 
Looking at this perpective, IMHO we should go with the number (0.25) 
instead of the boolean.


-- 
   Euler Taveira de Oliveira
   http://www.timbira.com/

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