Re: tracking commit timestamps

From: Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: 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>, Robert Haas <robertmhaas(at)gmail(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: 2014-11-05 16:34:40
Message-ID: 545A51A0.4080201@BlueTreble.com
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On 11/5/14, 10:30 AM, Andres Freund wrote:
>> Except that commit time is not guaranteed unique *even on a single
>> >system*. That's my whole point. If we're going to bother with all the
>> >commit time machinery it seems really silly to provide a way to
>> >uniquely order every commit.
> Well. I think that's the misunderstanding here. That's absolutely not
> what committs is supposed to be used for. For the replication stream
> you'd hopefully use logical decoding. That gives you the transaction
> data exactly in commit order.

So presumably you'd want to use logical decoding to insert into a table with a sequence on it, or similar?

I agree, that sounds like a better way to handle this. I think it's worth mentioning in the docs for commit_ts, because people WILL mistakenly try and use it to determine commit ordering.
--
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com

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