Subject: Re: [HACKERS] logical decoding of two-phase transactions
To: Andres Freund <andres@anarazel.de>
Cc: Nikhil Sontakke <nikhils@2ndquadrant.com>,
 Craig Ringer <craig@2ndquadrant.com>,
 Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 Simon Riggs <simon@2ndquadrant.com>,
 Petr Jelinek <petr.jelinek@2ndquadrant.com>,
 Sokolov Yura <y.sokolov@postgrespro.ru>,
 Stas Kelvich <s.kelvich@postgrespro.ru>,
 Dmitry Dolgov <9erthalion6@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>,
 Masahiko Sawada <sawada.mshk@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
 Robert Haas <robertmhaas@gmail.com>
References: 
 <CAMGcDxc9p7envO8t+29j=NdQXHoba6P1btfU0d3Xeiz7zT-Mvw@mail.gmail.com>
 <20180212162040.rsnlnysmf7n4yo7i@alap3.anarazel.de>
 <CAMGcDxeViP+R-OL7QhzUV9eKCVjURobuY1Zijik4Ay_Ddwo4Cg@mail.gmail.com>
 <20180302005343.zv6nsqimcujzjrcd@alap3.anarazel.de>
 <CAMsr+YEb-f1oG+1wGji_sgswRsVQYtVXuTbVH=nnY6thMfiCqA@mail.gmail.com>
 <CAMGcDxcD2fWqUwiPWGL_d-ie-CoGTVFAsgQvQ91H93q2Jc-mhA@mail.gmail.com>
 <CAMGcDxf9HHmDOti4-DSQTtGo48R4OMki+BktPn2uTOtGr4XomQ@mail.gmail.com>
 <c167340c-0751-d54b-0f32-fa83fd414863@2ndquadrant.com>
 <CAMGcDxcGtRXtF1r3VqddzHba+BTm7q8wbgEsyhmOFuDckMTZFQ@mail.gmail.com>
 <dd5a9cb7-bb10-cb5c-834e-08dc3ffc057f@2ndquadrant.com>
 <20180329215815.36xxakgujx4luo4m@alap3.anarazel.de>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <0925358a-e11d-51bc-c3c1-959ded75f604@2ndquadrant.com>
Date: Fri, 30 Mar 2018 00:23:00 +0200
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On 03/29/2018 11:58 PM, Andres Freund wrote:
> On 2018-03-29 23:52:18 +0200, Tomas Vondra wrote:
>>> I have added details about this in src/backend/storage/lmgr/README as
>>> suggested by you.
>>>
>>
>> Thanks. I think the README is a good start, but I think we also need to
>> improve the comments, which is usually more detailed than the README.
>> For example, it's not quite acceptable that LogicalLockTransaction and
>> LogicalUnlockTransaction have about no comments, especially when it's
>> meant to be public API for decoding plugins.
> 
> FWIW, for me that's ground to not accept the feature. Burdening output
> plugins with this will make their development painful (because they'll
> have to adapt regularly) and correctness doubful (there's nothing
> checking for the lock being skipped).  Another way needs to be found.
> 

The lack of docs/comments, or the fact that the decoding plugins would
need to do some lock/unlock operation?

I agree with the former, of course - docs are a must. I disagree with
the latter, though - there have been about no proposals how to do it
without the locking. If there are, I'd like to hear about it.

FWIW plugins that don't want to decode in-progress transactions don't
need to do anything, obviously.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services