| 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 |
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| Lists: | pgsql-hackers pgsql-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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