Re: FPW stats?

On Wed, May 02, 2018 at 12:22:34PM +0200, Dmitry Dolgov wrote:
> Recently I've heard people complaining that Postgres doesn't expose any
> statistics about how many full page writes happened during some time
> frame.

pg_waldump --stats?

> I guess it can be implemented in a more effective and optimized way, but with
> what I have right now first naive pgbench tests show that slowdown is about 3%.
> Before I'll dig into it more, it would be nice to hear your opinion about this
> idea -  does it make sense to have something like this?

The bar to add new fields into pgstat structures is usually quite high
depending on the location where those are added.  For example not so
long ago there was a patch discussed about adding more fields to
PgStat_StatTabEntry, which has been rejected as pgstat can be a problem
for users with many tables.  See here:
https://www.postgresql.org/message-id/1323.1511624064%40sss.pgh.pa.us

Your patch adds a new field to PgStat_StatDBEntry?  Wouldn't you
increase the bottleneck of deployments with many databases?  What's
actually your use case?
--
Michael