> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: 16 January 2004 21:50
> To: Martin Hampl
> Cc: pgsql-general@postgresql.org; Mark Cave-Ayland
> Subject: Re: [GENERAL] indexing with lower(...) -> queries
> are not optimised very well - Please Help
>
>
> Martin Hampl <Martin.Hampl@gmx.de> writes:
> > Am 21.11.2003 um 06:54 schrieb Tom Lane:
> >> [ bad plan for use of a functional index ]
> >>
> >> The rows estimate (and therefore also the cost estimate) is a
> >> complete guess in this situation, because the system keeps no
> >> statistics about the values of lower(word). Improving
> this situation
> >> is on the TODO list.
>
> > Any ideas when this will work? Is it difficult to implement?
>
> It strikes me as a small-but-not-trivial project. Possibly
> someone will get it done for 7.5. You can find some
> discussion in the pghackers archives, IIRC (look for threads
> about keeping statistics on functional indexes).
>
> This brings up a thought for Mark Cave-Ayland's project of
> breaking out the datatype dependencies in ANALYZE: it would
> be wise to ensure that the API for examine_attribute doesn't
> depend too much on the assumption that the value(s) being
> analyzed are part of the relation proper. They might be
> coming from a functional index, or even more likely being
> computed on-the-fly based on the definition of a functional
> index. Not sure what we'd want to change exactly, but it's
> something to think about before the API gets set in stone.
>
> regards, tom lane
Hi Tom/Martin,
I'm currently about 2/3rds of the way through writing my patch so things
are very nearly where I want them to be. In its current form it is just
the reorganisation and extension of what is already there, so I haven't
looked at the implications of functional indexes. It would be great if
the completed and checked patch can be applied so at least it gets out
there - then other developers can look at how this works for things like
functional indexes and put in the API changes required before the 7.5
feature freeze.
Cheers,
Mark.
---
Mark Cave-Ayland
Webbased Ltd.
Tamar Science Park
Derriford
Plymouth
PL6 8BX
England
Tel: +44 (0)1752 764445
Fax: +44 (0)1752 764446
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