From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: pgsql-hackers@lists.postgresql.org
Subject: ExecForceStoreMinimalTuple leaks memory like there's no tomorrow
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Content-ID: <365.1555382816.1@sss.pgh.pa.us>
Date: Mon, 15 Apr 2019 22:46:56 -0400
Message-ID: <366.1555382816@sss.pgh.pa.us>
Precedence: bulk

Using HEAD,

create table t1 as select generate_series(1,40000000) id;
vacuum analyze t1;
explain select * from t1, t1 t1b where t1.id = t1b.id;
-- should indicate a hash join
explain analyze select * from t1, t1 t1b where t1.id = t1b.id;

... watch the process's memory consumption bloat.  (It runs for
awhile before that starts to happen, but eventually it goes to
a couple of GB.)

It looks to me like the problem is that ExecHashJoinGetSavedTuple
calls ExecForceStoreMinimalTuple with shouldFree = true, and
ExecForceStoreMinimalTuple's second code branch simply ignores
the requirement to free the supplied tuple.

			regards, tom lane