On Mon, Feb 5, 2024 at 9:54 PM Greg Sabino Mullane <htamfids@gmail.com> wrote:
The pg_stat_*_tables tables idx_* columns has accumulated usage since the last time you started the postmaster.
Actually, those persist at restart - you can use
select datname, stats_reset from pg_stat_database;
to see when/if they were reset. You can look for zero/low entries in pg_stat_user_indexes.idx_scan to find unused indexes. Note that replicas maintain their own stats, so checking only the primary may cause a false positive.
I sql server we have this option to disable it and need to rebuild it to ensemble it
Sadly, PG does not have ALTER INDEX ... DISABLE;.
Not really sure what the purpose of that is in sql server,
To tell the system to stop using a specific index without having to drop the index.
Its only purpose is to make the DBA's life easier. IMNSHO, that's an excellent reason to have such a feature.
but Ron is correct, we have nothing equivalent. General usage in Postgres is to drop the index if it is unused. If you need to create it again, easy enough with CREATE INDEX CONCURRENTLY.
Unless it's blocked by existing readers. I've seen that more than a few times.
Keeping your schema changes in a VCS (e.g. git) is a good way to document when and why the index was dropped. I suppose in a pinch you could keep the old index around by sticking it in a table comment.
The ALTER INDEX ... DISABLE / ALTER INDEX ... REBUILD pair ensures that Mistakes Were Not Made.
You can't make the mistake of re-creating an index incorrectly if you didn't actually drop the index.