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Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: 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 17:14:39
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Lists: pgsql-hackerspgsql-patches
On Sun, 2008-01-27 at 21:04 -0500, Tom Lane wrote:
> [ redirecting thread to -hackers ]
> Neil Conway <neilc(at)samurai(dot)com> writes:
> > On Sun, 2008-01-27 at 21:54 +0000, Gregory Stark wrote:
> >> I liked the "synchronized_sequential_scans" idea myself.
> > I think that's a bit too long. How about "synchronized_scans", or
> > "synchronized_seqscans"?
> We have enable_seqscan already, so that last choice seems to fit in.

If we're going to have a GUC, we may as well make it as useful as

Currently we set synch scan on when the table is larger than 25% of
shared_buffers. So increasing shared_buffers can actually turn this
feature off.

Rather than having a boolean GUC, we should have a number and make the
parameter "synchronised_scan_threshold". This would then be the size of
a table above which we would perform synch scans. If its set to -1, then
this would be the same as "off" in all cases. The default value would be
25% of shared_buffers. (Think we can only do that at initdb time

If we do that, its clearly different from the enable_* parameters, so
the name is easier to decide ;-)

  Simon Riggs

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