Re: [PATCH] Tracking statements entry timestamp in pg_stat_statements

Hi Julien,

On Tue, 2021-03-23 at 15:03 +0800, Julien Rouhaud wrote:
> Note that you could also detect entries for which some counters
> decreased (e.g.
> the execution count), and in that case only use the current values.

Yes, but checking condition for several counters seems complicated
compared to check only one field.

> It should
> give the exact same results as what you will get with the first_seen
> column,
> except of course if some entry is almost never used and is suddenly
> used a lot
> after an explicit reset or an eviction and only until you perform
> your
> snapshot. I'm not sure that it's a very likely scenario though.
But it is possible, and we are guessing here. Storing a timestamp does
not seems too expensive to me, but it totally eliminates guessing, and
provides a clear view about the time interval we watching for this
specific statement.

> FTR that's how powa currently deals with reset/eviction.
PoWA sampling is much more frequent than pg_profile. For PoWA it is, of
cource, very unlikely scenario, but still possible.

--
Andrei Zubkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company