pg_stat_activity.waiting_start

Hi hackers,

We already have xact_start, query_start and backend_start
to get the timestamptz for when different things happened.

I would like to propose adding a fourth such column, "waiting_start",
which would tell how long time a backend has been waiting.

The column would be NULL when waiting=FALSE.

While it's trivial to write a script that just polls pg_stat_activity
every second and keeps tack of when a backend started
waiting by just checking for any new waiting=TRUE rows,
it would be more convenient to just get the information from
pg_stat_activity directly.

The use-case would be e.g. monitoring tools
when you want to know how long time queries are waiting.

--
Joel Jacobson