Re: Function index qeustion

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jonathan Bartlett <johnnyb(at)eskimo(dot)com>
Cc: Elielson Fontanezi <ElielsonF(at)prodam(dot)sp(dot)gov(dot)br>, "'Stephan Szabo'" <sszabo(at)megazone(dot)bigpanda(dot)com>, pgsql-general <pgsql-general(at)postgresql(dot)org>, pgsql-sql <pgsql-sql(at)postgresql(dot)org>
Subject: Re: Function index qeustion
Date: 2003-07-25 23:41:53
Message-ID: 9914.1059176513@sss.pgh.pa.us
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Jonathan Bartlett <johnnyb(at)eskimo(dot)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

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