Re: Duplicated LSN in ReorderBuffer

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Ildar Musin <ildar(at)adjust(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>
Subject: Re: Duplicated LSN in ReorderBuffer
Date: 2019-08-12 21:35:58
Message-ID: 20190812213558.GA1703@alvherre.pgsql
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On 2019-Aug-07, Andres Freund wrote:

> I think we would need to do this for all values of
> SnapBuildCurrentState() - after all the problem occurs because we
> *previously* didn't assign subxids to the toplevel xid. Compared to the
> cost of catalog changes, ReorderBufferAssignChild() is really cheap. So
> I don't think there's any problem just calling it unconditionally (when
> top_xid <> xid, of course).

BTW I wrote the code as suggested and it passes all the tests ... but I
then noticed that the unpatched code doesn't fail Ildar's original
pgbench-based test for me, either. So maybe my laptop is not powerful
enough to reproduce it, or maybe I'm doing something wrong.

I'm tempted to just push it, since it seems "obviously" more correct
than the original.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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