Date: Wed, 24 Nov 2021 19:15:59 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Andres Freund <andres@anarazel.de>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	Magnus Hagander <magnus@hagander.net>, pgsql-hackers@postgresql.org,
	Lukas Fittl <lukas@fittl.com>,
	Thomas Munro <thomas.munro@gmail.com>
Subject: Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and
 more?)
Message-ID: <20211125011559.GC17618@telsasoft.com>
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Thanks for working on this.  I was just trying to find something like
"pg_stat_checkpointer".

You wrote beentry++ at the start of two loops, but I think that's wrong; it
should be at the end, as in the rest of the file (or as a loop increment).
BackendStatusArray[0] is actually used (even though its backend has
backendId==1, not 0).  "MyBEEntry = &BackendStatusArray[MyBackendId - 1];"

You could put *_NUM_TYPES as the last value in these enums, like
NUM_AUXPROCTYPES, NUM_PMSIGNALS, and NUM_PROCSIGNALS:

+#define IOOP_NUM_TYPES (IOOP_WRITE + 1)
+#define IOPATH_NUM_TYPES (IOPATH_STRATEGY + 1)
+#define BACKEND_NUM_TYPES (B_LOGGER + 1)

There's extraneous blank lines in these functions:

+pgstat_sum_io_path_ops
+pgstat_report_live_backend_io_path_ops
+pgstat_recv_resetsharedcounter
+GetIOPathDesc
+StrategyRejectBuffer

This function is doubly-indented:

+pgstat_send_buffers_reset

As support for C99 is now required by postgres, variables can be declared as
part of various loops.

+       int                     io_path;
+       for (io_path = 0; io_path < IOPATH_NUM_TYPES; io_path++)

Rather than memset(), you could initialize msg like this.
PgStat_MsgIOPathOps msg = {0};

+pgstat_send_buffers(void)
+{
+       PgStat_MsgIOPathOps msg;
+
+       PgBackendStatus *beentry = MyBEEntry;
+
+       if (!beentry)
+               return;
+
+       memset(&msg, 0, sizeof(msg));

-- 
Justin