Horton

Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)

Justin Pryzby <pryzby@telsasoft.com>

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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>
Date: 2021-11-25T01:15:59Z
Lists: pgsql-hackers 
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

Commits

  1. Stabilize pg_stat_io writes test

  2. Fix flakey pg_stat_io test

  3. Suppress more compiler warnings in new pgstats code.

  4. Suppress compiler warnings in new pgstats code.

  5. Add tests for pg_stat_io

  6. Create regress_tblspc in test_setup

  7. Add pg_stat_io view, providing more detailed IO statistics

  8. pgstat: Track more detailed relation IO statistics

  9. pgstat: Infrastructure for more detailed IO statistics

  10. doc: Fix some issues in logical replication section

  11. Manual cleanup and pgindent of pgstat and bufmgr related code

  12. Have the planner consider Incremental Sort for DISTINCT

  13. Use actual backend IDs in pg_stat_get_backend_idset() and friends.

  14. Remove redundant call to pgstat_report_wal()

  15. Add BackendType for standalone backends

  16. Initialize backend status reporting during bootstrap.