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Re: Collect frequency statistics for arrays

From: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Noah Misch <noah(at)leadboat(dot)com>, Nathan Boley <npboley(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Collect frequency statistics for arrays
Date: 2012-02-29 20:54:35
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Lists: pgsql-hackers
On Thu, Mar 1, 2012 at 12:39 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> I am starting to look at this patch now.  I'm wondering exactly why the
> decision was made to continue storing btree-style statistics for arrays,
> in addition to the new stuff.  The pg_statistic rows for array columns
> tend to be unreasonably wide already, and as-is this patch will make
> them quite a lot wider.  I think it requires more than a little bit of
> evidence to continue storing stats that seem to have only small
> probability of usefulness.
> In particular, if we didn't store that stuff, we'd not need to widen the
> number of columns in pg_statistic, which would noticeably reduce both
> the footprint of the patch and the probability of breaking external
> code.

Initially, I used existing slots for new statistics, but I've changed this
after the first review:

Probably, btree statistics really does matter for some sort of arrays? For
example, arrays representing paths in the tree. We could request a subtree
in a range query on such arrays.

With best regards,
Alexander Korotkov.

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