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Re: Proposal: Commit timestamp

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jan Wieck <JanWieck(at)Yahoo(dot)com>
Cc: PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Proposal: Commit timestamp
Date: 2007-01-25 23:49:43
Message-ID: 13999.1169768983@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:
> To provide this data, I would like to add another "log" directory, 
> pg_tslog. The files in this directory will be similar to the clog, but 
> contain arrays of timestamptz values.

Why should everybody be made to pay this overhead?

> The COMMIT syntax will get extended to
>     COMMIT [TRANSACTION] [WITH TIMESTAMP <timestamptz>];
> The extension is limited to superusers and will override the normally 
> generated commit timestamp. This will be used to give the replicating 
> transaction on the replica the exact same timestamp it got on the 
> originating master node.

I'm not convinced you've even thought this through.  If you do that then
you have no guarantee of commit timestamp monotonicity on the slave
(if it has either multi masters or any locally generated transactions).
Since this is supposedly for a multi-master system, that seems a rather
fatal objection --- no node in the system will actually have commit
timestamp monotonicity.  What are you hoping to accomplish with this?

			regards, tom lane

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