Re: Index scan startup time

[Michael Stone <mstone+postgres(at)mathom(dot)us>]

On Thu, Mar 30, 2006 at 02:31:34PM +0200, Steinar H. Gunderson wrote:
> Well, it's logical enough; it scans along activity_id until it finds one with
> state=10000 or state=10001. You obviously have a _lot_ of records with low
> activity_id and state none of these two, so Postgres needs to scan all those
> records before it founds 100 it can output. This is the “startup cost” you're
> seeing.

Yes. And the estimates are bad enough (orders of magnitude) that I can't 
help but wonder whether pg could come up with a better plan with better 
statistics:

> > > >   ->  Index Scan using activity_pk on activity  (cost=0.00..40717259.91 rows=6538650 width=8) (actual time=207356.050..207356.722 rows=100 loops=1) Filter: ((state = 10000) OR (state = 10001))

Mike Stone