Re: [COMMITTERS] pgsql: Keep track of transaction commit timestamps

On 2014-12-29 12:50:23 +0200, Heikki Linnakangas wrote:
> On 12/29/2014 12:39 PM, Petr Jelinek wrote:
> >On 29/12/14 11:16, Andres Freund wrote:
> >>On 2014-12-29 12:06:07 +0200, Heikki Linnakangas wrote:
> >>>To be honest, I think this patch should be reverted. Instead, we should
> >>>design a system where extensions can define their own SLRUs to store
> >>>additional per-transaction information. That way, each extension can have as
> >>>much space per transaction as needed, and support functions that make most
> >>>sense with the information. Commit timestamp tracking would be one such
> >>>extension, and for this node ID stuff, you could have another one (or
> >>>include it in the replication extension).
> >>
> >>If somebody wants that they should develop it. But given that we, based
> >>on previous discussions, don't want to run user defined code in the
> >>relevant phase during transaction commit *and* replay I don't think it'd
> >>be all that easy to do it fast and flexible.
> >
> >Right, I would love to have custom SLRUs but I don't see it happening
> >given those two restrictions, otherwise I would write the CommitTs patch
> >that way in the first place...
>
> Transaction commit and replay can treat the per-transaction information as
> an opaque blob. It just needs to be included in the commit record, and
> replay needs to write it to the SLRU. That way you don't need to run any
> user-defined code in those phases.

Meh. Only if you want to duplicate the timestamps from the commits.

Greetings,

Andres Freund

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Andres Freund http://www.2ndQuadrant.com/
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