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

Hi,

> On Dec 8, 2020, at 1:06 PM, Masahiro Ikeda <ikedamsh(at)oss(dot)nttdata(dot)com> wrote:
>
> Hi,
>
> I propose to add wal write/fsync statistics to pg_stat_wal view.
> It's useful not only for developing/improving source code related to WAL
> but also for users to detect workload changes, HW failure, and so on.
>
> I introduce "track_wal_io_timing" parameter and provide the following information on pg_stat_wal view.
> I separate the parameter from "track_io_timing" to "track_wal_io_timing"
> because IIUC, WAL I/O activity may have a greater impact on query performance than database I/O activity.
>
> ```
> postgres=# SELECT wal_write, wal_write_time, wal_sync, wal_sync_time FROM pg_stat_wal;
> -[ RECORD 1 ]--+----
> wal_write | 650 # Total number of times WAL data was written to the disk
>
> wal_write_time | 43 # Total amount of time that has been spent in the portion of WAL data was written to disk
> # if track-wal-io-timing is enabled, otherwise zero
>
> wal_sync | 78 # Total number of times WAL data was synced to the disk
>
> wal_sync_time | 104 # Total amount of time that has been spent in the portion of WAL data was synced to disk
> # if track-wal-io-timing is enabled, otherwise zero
> ```
>
> What do you think?
> Please let me know your comments.
>
> Regards
> --
> Masahiro Ikeda
> NTT DATA CORPORATION<0001_add_wal_io_activity_to_the_pg_stat_wal.patch>

There is a no previous prototype warning for ‘fsyncMethodCalled’, and it now only used in xlog.c,
should we declare with static? And this function wants a boolean as a return, should we use
true/false other than 0/1?

+/*
+ * Check if fsync mothod is called.
+ */
+bool
+fsyncMethodCalled()
+{
+ if (!enableFsync)
+ return 0;
+
+ switch (sync_method)
+ {
+ case SYNC_METHOD_FSYNC:
+ case SYNC_METHOD_FSYNC_WRITETHROUGH:
+ case SYNC_METHOD_FDATASYNC:
+ return 1;
+ default:
+ /* others don't have a specific fsync method */
+ return 0;
+ }
+}
+

--
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ChengDu WenWu Information Technology Co.,Ltd.
Japin Li