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@oss.nttdata.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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Japin Li