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From: Peter Geoghegan <[email protected]>
To: Don Seiler <[email protected]>
Cc: Postgres General <[email protected]>
Subject: Re: Index Partition Size Double of its Table Partition?
Date: Wed, 30 Oct 2024 11:34:50 -0400
Message-ID: <CAH2-Wzmq+ZLkYFLq-WGJhd=xJ0UosQMuLCMbHXKcKucwsSL=eg@mail.gmail.com> (raw)
In-Reply-To: <CAHJZqBA83fBGjqXqF+rVbErdy2N0_zDEiLWJMrDUSKjKQOZi3Q@mail.gmail.com>
References: <CAHJZqBA83fBGjqXqF+rVbErdy2N0_zDEiLWJMrDUSKjKQOZi3Q@mail.gmail.com>

On Wed, Oct 30, 2024 at 11:24 AM Don Seiler <[email protected]> wrote:
> One thing worth mentioning is that the table is 4 columns, the index is on two of them and includes the other two. I can't think of an explanation for the index being so much larger than its table, especially compared to last month's index.
>
> Curious if anyone has any thoughts on what might be causing this.

You mentioned that this has 4 columns. Sounds like this could be a
"locally monotonically increasing index". I wonder if you're
benefiting from this optimization, though only inconsistently:

https://www.youtube.com/watch?v=p5RaATILoiE&t=2079s
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=f21668f3

Of course, this is only a guess. I vaguely recall a complaint that
sounded vaguely like yours, also involving partitioning.

--
Peter Geoghegan

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