From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jonathan Bartlett <johnnyb@eskimo.com>
Cc: Elielson Fontanezi <ElielsonF@prodam.sp.gov.br>
Cc: 'Stephan Szabo' <sszabo@megazone.bigpanda.com>
Cc: pgsql-general <pgsql-general@postgresql.org>
Cc: pgsql-sql <pgsql-sql@postgresql.org>
Subject: Re: Function index qeustion
Date: Fri, 25 Jul 2003 19:41:53 -0400
Message-ID: <9914.1059176513@sss.pgh.pa.us> (raw)
In-Reply-To: <Pine.GSU.4.44.0307251325080.14162-100000@eskimo.com>
References: <Pine.GSU.4.44.0307251325080.14162-100000@eskimo.com>
Jonathan Bartlett <johnnyb@eskimo.com> writes:
> 1) If you have an index on a cacheable function, does PostgreSQL use the
> index instead of calculating the results?
Not in general --- only for an indexscan lookup.
> 2) How does PostgreSQL know when to recompute the function?
Never. That's what the iscachable flag means: you are promising that
the function's output for given input never changes. If you aren't
prepared to make that promise, you cannot index the function.
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, johnnyb@eskimo.com, ElielsonF@prodam.sp.gov.br, sszabo@megazone.bigpanda.com, pgsql-general@postgresql.org
Subject: Re: Function index qeustion
In-Reply-To: <9914.1059176513@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox