From: Tom Lane <tgl@sss.pgh.pa.us>
To: Claudio Freire <klaussfreire@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Carlo Stonebanks <stonec.register@sympatico.ca>
Cc: pgsql-performance@postgresql.org
Subject: Re: Composite keys
Date: Mon, 31 Oct 2011 14:59:19 -0400
Message-ID: <5180.1320087559@sss.pgh.pa.us> (raw)
In-Reply-To: <CAGTBQpb1E7jQBn1S-yBCMo2w=V+iQRed-sDqNTj=cKPnYRicRg@mail.gmail.com>
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<CAGTBQpYMzj+xufEQBr7_aL3ZjZWaADU1oF40-ji8n8GcpZLj1A@mail.gmail.com>
<CA+TgmoY4Q+CyvxEVcNRjtMH_HeCP+uNXkrC8goVDVktsbAPNnA@mail.gmail.com>
<CAGTBQpb1E7jQBn1S-yBCMo2w=V+iQRed-sDqNTj=cKPnYRicRg@mail.gmail.com>
Claudio Freire <klaussfreire@gmail.com> writes:
> On Mon, Oct 31, 2011 at 2:08 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>>> Multicolumn indices on (c1, c2, ..., cn) can only be used on where
>>> clauses involving c1..ck with k<n.
>> I don't think that's true. I believe it can be used for a query that
>> only touches, say, c2. It's just extremely inefficient.
> Does postgres generate those kinds of plans?
Sure it does. It doesn't usually think they're efficient enough,
because they require full-index scans. But sometimes that's the
best you can do.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, klaussfreire@gmail.com, robertmhaas@gmail.com, stonec.register@sympatico.ca
Subject: Re: Composite keys
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