Re: tracking commit timestamps

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Steve Singer <steve(at)ssinger(dot)info>
Cc: Andres Freund <andres(at)2ndquadrant(dot)com>, Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Anssi Kääriäinen <anssi(dot)kaariainen(at)thl(dot)fi>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Jaime Casanova <jaime(at)2ndquadrant(dot)com>
Subject: Re: tracking commit timestamps
Date: 2014-11-07 23:35:16
Message-ID: 911880D7-9168-44B7-99DC-9F90DD4B9D86@gmail.com
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> On Nov 5, 2014, at 7:31 PM, Steve Singer <steve(at)ssinger(dot)info> wrote:
>> On 11/05/2014 05:43 PM, Andres Freund wrote:
>> On 2014-11-05 17:17:05 -0500, Steve Singer wrote:
>> Imo that's essentially a different feature. What you essentially would
>> need here is a 'commit sequence number' - but no timestamps. And
>> probably to be useful that number has to be 8 bytes in itself.
>
> I think this gets to the heart of some of the differing views people have expressed on this patch
>
> Is this patch supposed to:
>
> A) Add commit timestamp tracking but nothing more
>
> B) Add infrastructure to store commit timestamps and provide a facility for storing additional bits of data extensions might want to be associated with the commit
>
> C). Add commit timestamps and node identifiers to commits

Well put.

I think the authors of this patch are suffering from a certain amount of myopia. Commit timestamps are useful, but so are commit LSNs, and it makes little sense to me to suppose that we should have two different systems for those closely-related needs.

Like Andres, I think B is impractical, so let's just be honest and admit that C is what we're really doing. But let's add LSNs so the people who want that can be happy too.

...Robert

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