Re: Multiple FPI_FOR_HINT for the same block during killing btree index items

From: Peter Geoghegan <pg(at)bowt(dot)ie>
To: James Coleman <jtc331(at)gmail(dot)com>
Cc: Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Álvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Subject: Re: Multiple FPI_FOR_HINT for the same block during killing btree index items
Date: 2020-04-10 02:07:45
Message-ID: CAH2-Wzm2BPMD0JFVgUtpC-YGM6zjrwJJ6ixYOCSKr8QNoNuz3g@mail.gmail.com
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On Thu, Apr 9, 2020 at 6:47 PM James Coleman <jtc331(at)gmail(dot)com> wrote:
> I believe the write pattern to this table likely looks like:
> - INSERT
> - UPDATE
> - DELETE
> for every row. But tomorrow I can do some more digging if needed.

The pg_stats.null_frac for the column/index might be interesting here. I
believe that Active Record will sometimes generate created_at columns
that sometimes end up containing NULL values. Not sure why.

--
Peter Geoghegan

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