问题
Is there any way to calculate the amount of read per second on a Postgres table?
but what I need is that whether a table has any read at the moment. (If no, then I can safely drop it)
Thank you
回答1:
To figure out if the table is used currently, tun
SELECT pid
FROM pg_locks
WHERE relation = 'mytable'::regclass;
That will return the process ID of all backends using it.
To measure whether s table is used at all or not, run this query:
SELECT seq_scan + idx_scan + n_tup_ins + n_tup_upd + n_tup_del
FROM pg_stat_user_tables
WHERE relname = 'mytable';
Then repeat the query in a day. If the numbers haven't changed, nobody has used the table.
回答2:
Audit SELECT activity
My suggestion is to wrap mytable in a view (called the_view_to_use_instead in the example) which invokes a logging function upon every select and then use the view for selecting from, i.e.
select <whatever you need> from the_view_to_use_instead ...
instead of
select <whatever you need> from mytable ...
So here it is
create table audit_log (table_name text, event_time timestamptz);
create function log_audit_event(tname text) returns void language sql as
$$
insert into audit_log values (tname, now());
$$;
create view the_view_to_use_instead as
select mytable.*
from mytable, log_audit_event('mytable') as ignored;
Every time someone queries the_view_to_use_instead an audit record with a timestamp appears in table audit_log. You can then examine it in order to find out whether and when mytable was selected from and make your decision. Function log_audit_event can be reused in other similar scenarios. The average number of selects per second over the last 24 hours would be
select count(*)::numeric/86400
from audit_log
where event_time > now() - interval '86400 seconds';
来源：https://stackoverflow.com/questions/65217314/read-amount-on-a-postgres-table