Re: Hash join explain is broken

From: Andres Freund <andres(at)anarazel(dot)de>
To: Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Hash join explain is broken
Date: 2019-06-11 08:22:20
Message-ID: 20190611082220.eyhgjj47bj6jdkqp@alap3.anarazel.de
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Hi,

On 2019-06-11 00:45:57 -0700, Andres Freund wrote:
> On 2019-06-10 21:28:12 +0300, Alexander Korotkov wrote:
> > After 5f32b29c explain of Hash Join sometimes triggers an error.
> >
> > Simple reproduction case is below.
>
> Thanks for finding. I've created an open issue for now.

I am too tired to look further into this. I suspect the only reason we
didn't previously run into trouble with the executor stashing hashkeys
manually at a different tree level with:
((HashState *) innerPlanState(hjstate))->hashkeys
is that hashkeys itself isn't printed...

If done properly, the expression would actually reside in the Hash node
itself, rather than ExecInitHashJoin() splitting up the join condition
itself, and moving it into the HashState.

Greetings,

Andres Freund

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