Re: separating improperly grouped page views

On Sun, 17 Jun 2007, Jeff Frost wrote:

> -------------------------------------------------------------------------------------------------------------------------------------
> Seq Scan on page_view pv1 (cost=0.00..11529031.34 rows=3580205 width=239)
> SubPlan
> -> Result (cost=1.58..1.59 rows=1 width=0)
> InitPlan
> -> Limit (cost=0.00..1.58 rows=1 width=8)
> -> Index Scan Backward using page_view_visit_id_stamp_idx
> on page_view pv2 (cost=0.00..625.39 rows=397 width=8)
> Index Cond: ((visit_id = $0) AND (stamp < $1))
> Filter: (stamp IS NOT NULL)
> -> Result (cost=1.58..1.59 rows=1 width=0)
> InitPlan
> -> Limit (cost=0.00..1.58 rows=1 width=8)
> -> Index Scan Backward using page_view_visit_id_stamp_idx
> on page_view pv2 (cost=0.00..625.39 rows=397 width=8)
> Index Cond: ((visit_id = $0) AND (stamp < $1))
> Filter: (stamp IS NOT NULL)
> (14 rows)
>
> Compared to:
>
>
> -------------------------------------------------------------------------------------------------------------------------------
> Seq Scan on page_view pv1 (cost=0.00..2622541458.55 rows=3596473 width=237)
> SubPlan
> -> Result (cost=364.56..364.57 rows=1 width=0)
> InitPlan
> -> Limit (cost=0.00..364.56 rows=1 width=8)
> -> Index Scan Backward using page_view_stamp_idx on
> page_view pv2 (cost=0.00..153481.58 rows=421 width=8)
> Index Cond: (stamp < $1)
> Filter: ((stamp IS NOT NULL) AND (visit_id = $0))
> -> Result (cost=364.56..364.57 rows=1 width=0)
> InitPlan
> -> Limit (cost=0.00..364.56 rows=1 width=8)
> -> Index Scan Backward using page_view_stamp_idx on
> page_view pv2 (cost=0.00..153481.58 rows=421 width=8)
> Index Cond: (stamp < $1)
> Filter: ((stamp IS NOT NULL) AND (visit_id = $0))
> (14 rows)

And throwing the ORDER BY back in reduces the cost even more!

QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------
Subquery Scan x (cost=0.00..5815824.15 rows=3629753 width=1186)
-> Index Scan using page_view_visit_idx on page_view pv1 (cost=0.00..5743229.09 rows=3629753 width=237)
SubPlan
-> Result (cost=1.51..1.52 rows=1 width=0)
InitPlan
-> Limit (cost=0.00..1.51 rows=1 width=8)
-> Index Scan Backward using page_view_visit_id_stamp_idx on page_view pv2 (cost=0.00..608.41 rows=402 width=8)
Index Cond: ((visit_id = $0) AND (stamp < $1))
Filter: (stamp IS NOT NULL)
(9 rows)

Now we only have to do that index scan once. :-) I had foolishly taken that
out to see if the sort was killing me and forgot to put it back in.

So now it's:

Subquery Scan x (cost=0.00..5815824.15 rows=3629753 width=1186)
vs
Seq Scan on page_view pv1 (cost=0.00..11529031.34 rows=3580205 width=239)
vs
Seq Scan on page_view pv1 (cost=0.00..2622541458.55 rows=3596473 width=237)

--
Jeff Frost, Owner <jeff(at)frostconsultingllc(dot)com>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954