Re: [PATCHES] Proposed patch: synchronized_scanning GUC variable - Mailing list pgsql-hackers

From Hans-Juergen Schoenig
Subject Re: [PATCHES] Proposed patch: synchronized_scanning GUC variable
Date
Msg-id 93EDC9E5-06FD-4EE0-AF0D-117310024B81@cybertec.at
Whole thread Raw
In response to Re: [PATCHES] Proposed patch: synchronized_scanning GUC variable  (Simon Riggs <simon@2ndquadrant.com>)
List pgsql-hackers

On Jan 28, 2008, at 6:14 PM, Simon Riggs wrote:

On Sun, 2008-01-27 at 21:04 -0500, Tom Lane wrote:
[ redirecting thread to -hackers ]

Neil Conway <neilc@samurai.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 ;-)


+1
This is in fact a lot more flexible and transparent.
It gives us a lot more control over the process and it is easy to explain / understand.

best regards,

hans

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