Re: Inconsistency in reporting checkpointer stats

On Wed, Dec 14, 2022 at 04:54:53PM +0530, Bharath Rupireddy wrote:
> Indeed PendingCheckpointerStats.buf_written_checkpoints needs to count
> buffer writes in SlruInternalWritePage(). However, does it need to be
> done immediately there? The stats will not be visible to the users
> until the next pgstat_report_checkpointer(). Incrementing
> buf_written_checkpoints in BufferSync() makes sense as the
> pgstat_report_checkpointer() gets called in there via
> CheckpointWriteDelay() and it becomes visible to the user immediately.
> Have you checked if pgstat_report_checkpointer() gets called while the
> checkpoint calls SlruInternalWritePage()? If not, then you can just
> assign ckpt_bufs_written to buf_written_checkpoints in
> LogCheckpointEnd() like its other friends
> checkpoint_write_time and checkpoint_sync_time.

/* If part of a checkpoint, count this as a buffer written. */
if (fdata)
CheckpointStats.ckpt_bufs_written++;
+ PendingCheckpointerStats.buf_written_checkpoints++;
Also, the proposed patch would touch PendingCheckpointerStats even
when there is no fdata, aka outside the context of a checkpoint or
shutdown sequence..
--
Michael