Re: Collect frequency statistics for arrays

On Wed, Feb 29, 2012 at 5:43 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Nathan Boley <npboley(at)gmail(dot)com> writes:
>> On Wed, Feb 29, 2012 at 12:39 PM, 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.
>
>> If I understand you're suggestion, queries of the form
>
>> SELECT * FROM rel
>> WHERE ARRAY[ 1,2,3,4 ] <= x
>>      AND x <=ARRAY[ 1, 2, 3, 1000];
>
>> would no longer use an index. Is that correct?
>
> No, just that we'd no longer have statistics relevant to that, and would
> have to fall back on default selectivity assumptions.  Do you think that
> such applications are so common as to justify bloating pg_statistic for
> everybody that uses arrays?

I confess I am nervous about ripping this out. I am pretty sure we
will get complaints about it. Performance optimizations that benefit
group A at the expense of group B are always iffy, and I'm not sure
the case of using an array as a path indicator is as uncommon as you
seem to think.

--
Robert Haas
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