On Wed, May 19, 2010 at 10:53 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Matthew Wakeling <matthew(at)flymine(dot)org> writes:
>> On Tue, 18 May 2010, Scott Marlowe wrote:
>>> Aggregate (cost=902.41..902.42 rows=1 width=4)
>>> -> Merge Join (cost=869.97..902.40 rows=1 width=4)
>>> Merge Cond: (f.eid = ev.eid)
>>> -> Index Scan using files_eid_idx on files f
>>> (cost=0.00..157830.39 rows=3769434 width=8)
>
>> Okay, that's weird. How is the cost of the merge join only 902, when the
>> cost of one of the branches 157830, when there is no LIMIT?
>
> It's apparently estimating (wrongly) that the merge join won't have to
> scan very much of "files" before it can stop because it finds an eid
> value larger than any eid in the other table. So the issue here is an
> inexact stats value for the max eid.
That's a big table. I'll try cranking up the stats target for that
column and see what happens. Thanks!