From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
cc: Euler Taveira <euler@timbira.com.br>, James Tomson <james@pushd.com>,
        pgsql-bugs@lists.postgresql.org, Eric Jensen <ej@pushd.com>
Subject: Re: invalid memory alloc request size from pg_stat_activity?
In-reply-to: <20190507145513.GA7111@alvherre.pgsql>
References: <20190507145513.GA7111@alvherre.pgsql>
Comments: In-reply-to Alvaro Herrera <alvherre@2ndquadrant.com>
	message dated "Tue, 07 May 2019 10:55:13 -0400"
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Date: Tue, 07 May 2019 11:14:27 -0400
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Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Hmm, but 102400 is only 100kB, nowhere near the 1GB-1 limit, so there's
> something odd going on there.

I can reproduce the described behavior by also setting max_connections
to something around 16K.

Now, it seems pretty silly to me to be burning in excess of 1GB of shmem
just for the current-query strings, and then that much again in every
backend that reads pg_stat_activity.  But should we be telling people they
can't do it?  I'm working on a patch to use MemoryContextAllocHuge for
the "localactivity" buffer in pgstat_read_current_status.  It might seem
dumb now, but perhaps in ten years it'll be common.

			regards, tom lane