From: Tom Lane <tgl@sss.pgh.pa.us>
To: Kyle Bateman <kyle@actarg.com>
Cc: pgsql-sql@postgresql.org, Florian Weimer <fweimer@bfk.de>
Subject: Re: Using bitmap index scans-more efficient
Date: Mon, 14 Aug 2006 21:53:37 -0400
Message-ID: <27367.1155606817@sss.pgh.pa.us> (raw)
In-Reply-To: <44E11E1A.8020507@actarg.com>
References: <44DF6582.4000806@actarg.com>
<82mza77rch.fsf@mid.bfk.de>
<44E11E1A.8020507@actarg.com>
Kyle Bateman <kyle@actarg.com> writes:
> But I'm assuming that using an interval-encoded project tree, I would
> have to do something like the following to get a progency group:
> select * from ledger l, proj p where p.proj_id = l.proj and p.left >
> 1234 and p.right < 2345;
btree has no idea about the constraint (that I imagine exists) that left
<= right. If you're just doing a simple index on (left, right) then the
above query requires scanning all index entries with left > 1234. It
would probably help to say
select * from ledger l, proj p where p.proj_id = l.proj and
p.left > 1234 and p.left < 2345 and p.right < 2345;
so that you can constrain the range of "left" values scanned.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, kyle@actarg.com, fweimer@bfk.de
Subject: Re: Using bitmap index scans-more efficient
In-Reply-To: <27367.1155606817@sss.pgh.pa.us>
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