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Re: Function Scan costs

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Andy Halsall <halsall_andy(at)hotmail(dot)com>
Cc: "postgresql (dot)org novice list" <pgsql-novice(at)postgresql(dot)org>
Subject: Re: Function Scan costs
Date: 2012-06-27 23:33:51
Message-ID: 1340840031.32226.12.camel@sussancws0025 (view raw, whole thread or download thread mbox)
Lists: pgsql-novice
On Wed, 2012-06-27 at 15:56 +0000, Andy Halsall wrote:
> I'm calling functions via libpq. I've noticed that in the EXPLAIN
> analysis the time for the Function Scan is high relative to that of
> the actual query. In the example below (if I'm reading it correctly),
> the query seems to take just 0.022 ms whereas the time allocated to
> "Function Scan is 0.483ms. Is this to do with parsing original query
> and substituting params? Could somebody please explain? Thanks.

The times involved are quite small so it's hard to speculate on exactly
what's causing the difference (if there is a real difference).

If I had to guess, I would say that it's because a set-returning
function (SRF) always materializes the entire result. That's a
limitation of SRFs, and you might consider a foreign table instead if it
suits your needs.

	Jeff Davis

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Subject: Re: The use of cpu_index_tuple_cost by the query planner
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