Re: Tracking last scan time

On Wed, Aug 31, 2022 at 11:56:29AM -0700, Andres Freund wrote:
> Hi,
>
> On 2022-08-31 19:52:49 +0200, Matthias van de Meent wrote:
> > As for having a lower granularity and preventing the
> > one-syscall-per-Relation issue, can't we reuse the query_start or
> > state_change timestamps that appear in pg_stat_activity (potentially
> > updated immediately before this stat flush), or some other per-backend
> > timestamp that is already maintained and considered accurate enough
> > for this use?
>
> The problem is that it won't change at all for a query that runs for a week -
> and we'll report the timestamp from a week ago when it finally ends.
>
> But given this is done when stats are flushed, which only happens after the
> transaction ended, we can just use GetCurrentTransactionStopTimestamp() - if
> we got to flushing the transaction stats we'll already have computed that.

Oh, good point --- it is safer to show a more recent time than a too-old
time.

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Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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