Horton

RE: About to add WAL write/fsync statistics to pg_stat_wal view

Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>

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From: "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>
To: 'Masahiro Ikeda' <ikedamsh@oss.nttdata.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-01-22T02:54:17Z
Lists: pgsql-hackers 
Dear Ikeda-san,

This patch cannot be applied to the HEAD, but anyway I put a comment.

```
+	/*
+	 * Measure i/o timing to fsync WAL data.
+	 *
+	 * The wal receiver skip to collect it to avoid performance degradation of standy servers.
+	 * If sync_method doesn't have its fsync method, to skip too.
+	 */
+	if (!AmWalReceiverProcess() && track_wal_io_timing && fsyncMethodCalled())
+		INSTR_TIME_SET_CURRENT(start);
```

I think m_wal_sync_time should be collected even if the process is WalRecevier.
Because all wal_fsync should be recorded, and
some performance issues have been aleady occurred if track_wal_io_timing is turned on.
I think it's strange only to take care of the walrecevier case.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED

Commits

  1. Send statistics collected during shutdown checkpoint to the stats collector.

  2. Force to send remaining WAL stats to the stats collector at walwriter exit.

  3. Track total amounts of times spent writing and syncing WAL data to disk.

  4. Retry short writes when flushing WAL.