On 29.06.2018 15:48, Robert Haas wrote:
On Wed, Jun 27, 2018 at 10:27 PM, Michael Paquier <mich...@paquier.xyz> wrote:
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.
Are there other instances of fsync() that also need to be covered?
Syncing database files is already monitored (in mdsync and FileFlush).
If we grep for pg_fsync occurrences in Postgres code, then the only
place where pgstat_report_wait_start is not called before is
issue_xlog_fsync in xlog.c
--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
