From: Robert Haas <robertmhaas@gmail.com>
To: Anj Adu <fotographs@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: partition pruning
Date: Thu, 4 Mar 2010 17:40:02 -0500
Message-ID: <603c8f071003041440r2ec69a9dw91153f35ab2b3d53@mail.gmail.com> (raw)
In-Reply-To: <f2fd819a1003011129h2222281fqa67bc45e051c6dd8@mail.gmail.com>
References: <f2fd819a1003011129h2222281fqa67bc45e051c6dd8@mail.gmail.com>
On Mon, Mar 1, 2010 at 2:29 PM, Anj Adu <fotographs@gmail.com> wrote:
> When I use intervals in my query e.g col1 between current_timestamp -
> interval '10 days' and current_timestamp...the optimizer checks ALL
> partitions whereas if I use col1 between 2 hardcoded dates..only
> the applicable partitions are scanned.
Yep. This is one example of a more general principle:
constant-folding happens before planning, but anything more complex
has to wait until execution time. So the plan can't take into account
the value of current_timestamp in forming the plan.
Unfortunately I don't think there's really any easy way around this:
you have to do select current_timestamp, current_timestamp - interval
'10 days' first and then build & execute a new query.
...Robert
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To: pgsql-performance@postgresql.org
Cc: robertmhaas@gmail.com, fotographs@gmail.com
Subject: Re: partition pruning
In-Reply-To: <603c8f071003041440r2ec69a9dw91153f35ab2b3d53@mail.gmail.com>
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