Re: Adding locks statistics

Great idea. +1. Here is a quick overall review to get things started.

Meta:
patch did not apply via "git apply". Also has carriage returns (e.g. DOS file), and some errant whitespace. Seems to pass pgindent, though.

Name:
I think the name would read better as pg_stat_locks, especially as it returns multiple rows.

Docs: seem good. Needs a section on how to reset via
SELECT pg_stat_reset_shared('lock');
Also plural better here ('locks')

Code:

+ * Copyright (c) 2021-2025, PostgreSQL Global Development Group

If a new file, we can simply say 2025?

+ LWLock locks[LOCKTAG_LAST_TYPE + 1];
+ PgStat_Lock stats;

Adding a lock to the system that counts locks! :) (just found amusing, not a comment)

-#define PGSTAT_KIND_SLRU 11
-#define PGSTAT_KIND_WAL 12
+#define PGSTAT_KIND_LOCK 11
+#define PGSTAT_KIND_SLRU 12
+#define PGSTAT_KIND_WAL 13

Why not just add LOCK as #13?

What about the overhead of maintaining this system? I know it's overall very lightweight, but from my testing, the relation locktype in particular is very, very busy. Busier than I realized until I saw it in this useful view!