Re: Proposal: "Causal reads" mode for load balancing reads without stale data

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Thom Brown <thom(at)linux(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de>
Subject: Re: Proposal: "Causal reads" mode for load balancing reads without stale data
Date: 2016-03-29 17:04:24
Message-ID: CA+TgmoY8bunyH0MV=P81XPe3vOrfOjk9TaqJmnZmW02sM3U+aQ@mail.gmail.com
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On Tue, Mar 29, 2016 at 3:17 AM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> OK, so I am switching this patch as "Ready for committer", for 0001.
> It is in better shape now.

Well... I have a few questions yet.

The new argument to SyncRepWaitForLSN is called "bool commit", but
RecordTransactionAbortPrepared passes true. Either it should be
passing false, or the parameter is misnamed or at the least in need of
a better comment.

I don't understand why this patch is touching the abort paths at all.
XactLogAbortRecord sets XACT_COMPLETION_SYNC_APPLY_FEEDBACK, and
xact_redo_abort honors it. But surely it makes no sense to wait for
an abort to become visible.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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