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Re: Proposed fixes for planner regressions from June torelease

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
Cc: pgsql-patches(at)postgreSQL(dot)org
Subject: Re: Proposed fixes for planner regressions from June torelease
Date: 2006-12-11 20:33:57
Message-ID: 15646.1165869237@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
"Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> Are Arjen's tests on prepared queries?

No.

> Does that change anything? We shy
> away from indexes on prepared queries too much already, important when
> the consequence of doing so is an O(N) seqscan rather than an O(logN)
> indexscan.

Changing that will require far more extensive changes than twiddling a
few cost estimates.

> The cost of initiating an index scan is a cause for concern, but it
> seems reasonable to get it accurate. I'd like to perform some of that
> work at planning time, not at scan time, when it is possible for us to
> do so. Simple indexed, planned queries shouldn't need to pay that cost
> repeatedly.

Isn't this opinion in direct contradiction to your previous paragraph?
If you want the thing to be more flexible about plans involving unknown
parameter values, then you have to push work towards the runtime end,
not towards the planner.

			regards, tom lane

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