From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: weird hash plan cost, starting with pg10
In-reply-to: <20200323165059.GA24950@alvherre.pgsql>
References: <20200323165059.GA24950@alvherre.pgsql>
Comments: In-reply-to Alvaro Herrera <alvherre@2ndquadrant.com>
	message dated "Mon, 23 Mar 2020 13:50:59 -0300"
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Date: Mon, 23 Mar 2020 13:00:59 -0400
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Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> While messing with EXPLAIN on a query emitted by pg_dump, I noticed that
> current Postgres 10 emits weird bucket/batch/memory values for certain
> hash nodes:

>                          ->  Hash  (cost=3D0.11..0.11 rows=3D10 width=3D=
12) (actual time=3D0.002..0.002 rows=3D1 loops=3D8)
>                                Buckets: 2139062143  Batches: 2139062143 =
 Memory Usage: 8971876904722400kB
>                                ->  Function Scan on unnest init_1  (cost=
=3D0.01..0.11 rows=3D10 width=3D12) (actual time=3D0.001..0.001 rows=3D1 l=
oops=3D8)

Looks suspiciously like uninitialized memory ...

> The complete query is:

Reproduces here, though oddly only a couple of the several hash subplans
are doing that.

I'm not planning to dig into it right this second either.

			regards, tom lane