Re: [HACKERS] pg_stat_wal_write statistics view

On Tue, Sep 12, 2017 at 9:06 AM, Haribabu Kommi
<kommi.haribabu@gmail.com> wrote:
>
>
> On Tue, Sep 12, 2017 at 2:04 AM, Kuntal Ghosh <kuntalghosh.2007@gmail.com>
> wrote:
>
Thanks for the patch.
+ * Check whether the current process is a normal backend or not.
+ * This function checks for the background processes that does
+ * some WAL write activity only and other background processes
+ * are not considered. It considers all the background workers
+ * as WAL write activity workers.
+ *
+ * Returns false - when the current process is a normal backend
+ *        true - when the current process a background process/worker
+ */
+static bool
+am_background_process()
+{
+   /* check whether current process is a background process/worker? */
+   if (!AmBackgroundWriterProcess() ||
+       !AmCheckpointerProcess() ||
+       !AmStartupProcess() ||
+       !IsBackgroundWorker ||
+       !am_walsender ||
+       !am_autovacuum_worker)
+   {
+       return false;
+   }
+
+   return true;
+}
I think you've to do AND operation here instead of OR. Isn't it?
Another point is that, the function description could start with
'Check whether the current process is a background process/worker.'

> There is an overhead with IO time calculation. Is the view is good
> enough without IO columns?
I'm not sure how IO columns are useful for tuning the WAL write/fsync
performance from an user's perspective. But, it's definitely useful
for developing/improving stuffs in XLogWrite.

>
> And also during my tests, I didn't observe any other background
> processes performing the xlogwrite operation, the values are always
> zero. Is it fine to merge them with backend columns?
>
Apart from wal writer process, I don't see any reason why you should
track other background processes separately from normal backends.
However, I may be missing some important point.