Re: [PATCH] Don't block HOT update by BRIN index

On 6/30/21 12:53 AM, Josef Šimánek wrote:
> st 30. 6. 2021 v 0:31 odesílatel Josef Šimánek <josef(dot)simanek(at)gmail(dot)com> napsal:
>>
>> Hello!
>>
>> Tomáš Vondra has shared a few ideas to improve BRIN index in czech
>> PostgreSQL mail list some time ago [1 , in czech only]. This is first
>> try to implement one of those ideas.
>>
>> Currently BRIN index blocks HOT update even it is not linked tuples
>> directly. I'm attaching the initial patch allowing HOT update even on
>> BRIN indexed columns. This patch went through an initial review on
>> czech PostgreSQL mail list [1].
>
> I just found out current patch is breaking partial-index isolation
> test. I'm looking into this problem.
>

The problem is in RelationGetIndexAttrBitmap - the existing code first
walks indnatts, and builds the indexattrs / hotblockingattrs. But then
it also inspects expressions and the predicate (by pull_varattnos), and
the patch fails to do that for hotblockingattrs. Which is why it fails
for partial-index, because that uses an index with a predicate.

So there needs to be something like:

if (indexDesc->rd_indam->amhotblocking)
pull_varattnos(indexExpressions, 1, &hotblockingattrs);

if (indexDesc->rd_indam->amhotblocking)
pull_varattnos(indexPredicate, 1, &hotblockingattrs);

This fixes the failure for me.

regards

--
Tomas Vondra
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