Re: Temporarily very slow planning time after a big delete

On Tue, May 21, 2019 at 11:17 AM Peter Geoghegan <[email protected]> wrote:

> On Tue, May 21, 2019 at 11:16 AM Walter Smith <[email protected]> wrote:
> > It occurs to me that is a somewhat unusual index -- it tracks
> unprocessed notifications so it gets an insert and delete for every row,
> and is normally almost empty.
>
> Is it a very low cardinality index? In other words, is the total
> number of distinct keys rather low? Not just at any given time, but
> over time?


Very low. Probably less than ten over all time. I suspect the only use of
the index is to rapidly find the processed=false rows, so the
notifiable_type value isn’t important, really. It would probably work just
as well on any other column.

— Walter