Re: Monitoring time of fsyncing WALs

On Wed, Jun 27, 2018 at 07:32:18PM +0300, Konstantin Knizhnik wrote:
> I wonder why we are monitoring time of writing to WAL, but not time of
> fsyncing WAL segments?
> Is there are principle reason for it or just because nobody added it yet?
> If so, please find very small patch which adding WAIT_EVENT_WAL_FSYNC event
> type.

Let's name it WAIT_EVENT_WAL_SYNC as it is more consistent with the
other wait events of the same type, and also list the wait event
alphabetically everywhere this is added. I have also reworded the
documentation to be more consistent.

> Our engineers in PgPro complain me that there is no information about time
> spent in syncing WALs...
> Unfortunately Postgres still is not able to aggregate this statistic. But at
> least we have pg_wait_sampling extension for it:
> https://github.com/postgrespro/pg_wait_sampling

Complain justified. It is a bit too late for v11 I think though, so
let's wait for v12 to open for business, and then I'll apply the patch
at if there are no objections until then.

Attached is an updated patch.
--
Michael