Re: per backend WAL statistics

On Wed, Jan 08, 2025 at 11:11:59AM +0000, Bertrand Drouvot wrote:
> Yeah, that's more elegant as it also means that the main callback will not change
> (should we add even more stats in the future). Done that way in v2 attached.

I've put my hands on v2-0002 to begin with something.

+/* flag bits for different types of statistics to flush */
+#define PGSTAT_FLUSH_IO (1 << 0) /* Flush I/O statistics */
+#define PGSTAT_FLUSH_ALL (PGSTAT_FLUSH_IO)

These are located and used only in pgstat_backend.c. It seems to me
that we'd better declare them in pgstat_internal.h and extend the
existing pgstat_flush_backend() with an argument so as callers can do
what they want.

+ /* Get our own entry_ref if not provided */
+ if (!entry_ref)
+ entry_ref = pgstat_get_entry_ref(PGSTAT_KIND_BACKEND, InvalidOid,
+ MyProcNumber, false, NULL);

This relates to the previous remark, actually, where I think that it
is cleaner to have pgstat_flush_backend() do pgstat_get_entry_ref(),
same way as HEAD, and just pass down the flags. pgstat_flush_backend
cannot call directly pgstat_backend_flush_cb(), of course, so I've
settled down to a new pgstat_flush_backend_entry() that handles the
entry locking. This comes at the cost of pgstat_flush_backend_entry()
requiring an extra pgstat_tracks_backend_bktype(), which is not a big
issue, and the patch gets a bit shorter.
--
Michael