Re: Introduce a new view for checkpointer related stats

Hi,

On 11/17/22 1:51 PM, Bharath Rupireddy wrote:
> Hi,
> 
> pg_stat_bgwriter view currently reports checkpointer stats as well. It
> is that way because historically checkpointer was part of bgwriter
> until the commits 806a2ae and bf405ba, that went into PG 9.2,
> separated them out. I think it is time for us to separate checkpointer
> stats to its own view. I discussed it in another thread [1] and it
> seems like there's an unequivocal agreement for the proposal.
> 
> I'm attaching a patch introducing a new pg_stat_checkpointer view,
> with this change the pg_stat_bgwriter view only focuses on bgwriter
> related stats. The patch does mostly mechanical changes. I'll add it
> to CF in a bit.
> 
> Thoughts?

+1 for the dedicated view.

+  <para>
+   The <structname>pg_stat_checkpointer</structname> view will always have a
+   single row, containing global data for the cluster.
+  </para>

what about "containing data about checkpointer activity of the cluster"? (to provide more "details" (even if that seems
obviousgiven the name of the view) and be consistent with the pg_stat_wal description too).
 
And if it makes sense to you, While at it, why not go for "containing data about bgwriter activity of the cluster" for
pg_stat_bgwritertoo?
 

+CREATE VIEW pg_stat_checkpointer AS
+    SELECT
+        pg_stat_get_timed_checkpoints() AS checkpoints_timed,
+        pg_stat_get_requested_checkpoints() AS checkpoints_req,
+        pg_stat_get_checkpoint_write_time() AS checkpoint_write_time,
+        pg_stat_get_checkpoint_sync_time() AS checkpoint_sync_time,
+        pg_stat_get_buf_written_checkpoints() AS buffers_checkpoint,
+        pg_stat_get_buf_written_backend() AS buffers_backend,
+        pg_stat_get_buf_fsync_backend() AS buffers_backend_fsync,
+        pg_stat_get_checkpointer_stat_reset_time() AS stats_reset;

I don't think we should keep the checkpoints_ prefix (or _checkpoint suffix) in the column names now that they belong
toa dedicated view (also the pg_stat_bgwriter view's columns don't have a
 
bgwriter prefix/suffix).

And while at it, I'm not sure the wal_ suffix in pg_stat_wal make sense too.

The idea is to have consistent naming between the views and their columns: I'd vote without prefix/suffix.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com