Re: [PATCHES] Proposed patch: synchronized_scanning GUC variable

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
possible.

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
currently).

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

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