Re: Do I understand commit timestamps correctly?

On 2020-May-13, Chapman Flack wrote:

> Getting around to trying it out, simply changing the setting in
> postgresql.conf before starting the server does not seem sufficient:
> once it comes online, it has track_commit_timestamp on, but has not
> populated the cache from transactions it applied during recovery.

Ah. I had not realized that that was what you wanted to do.

> On the other hand, changing the setting in postgresql.conf *and*
> poking a 1 in the track_commit_timestamp byte in pg_control,
> and fudging the CRC accordingly, *then* starting the server, does
> seem to do just as I had hoped. Nothing seems to complain or fall over,
> and the transactions recovered from WAL now have timestamps visible
> with pg_xact_commit_timestamp().

Nice hack. I guess you'd sooner have a supported way to enable the bit
in pg_control. Is there a use case for this?

--
Álvaro Herrera https://www.2ndQuadrant.com/
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