From: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
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To: | "Greg Smith" <greg(at)2ndquadrant(dot)com>, "Dan Ports" <drkp(at)csail(dot)mit(dot)edu> |
Cc: | "Vlad Arkhipov" <arhipov(at)dc(dot)baikal(dot)ru>, <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Predicate locking |
Date: | 2011-05-04 02:07:57 |
Message-ID: | 4DC06EAD020000250003D213@gw.wicourts.gov |
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Lists: | pgsql-hackers |
Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> However, if I increase the generate_series to create 349 rows (or
> more) instead, it works.
> I don't fully understand why this attempt I tried to do that is
> working the way it does though.
Check where the plan goes from a table scan to an indexed access.
Also look at what is showing for SIRead locks in pg_locks as you go.
Between those two bits of information, it should become apparent.
> I don't think Vlad is being unreasonable here; he's provided a
> test case demonstrating the behavior he'd like to see, and shown
> it doesn't work as expected.
... on a toy table with contrived values. How different is this
from the often-asked question about why a query against a four-line
table is not using the index they expect, and how can we expect it
to scale if it doesn't? I agree that it's not unreasonable for
someone to ask either question. If my response falls short, I'm
game to try again.
-Kevin
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