Re: select slows from 3 seconds to 30 seconds

On Saturday 05 May 2007 01:57, Tom Lane wrote:
> Gary Stainburn <gary(dot)stainburn(at)ringways(dot)co(dot)uk> writes:
> > I have the query below which when run takes approx 3 seconds. However
> > when I add the condition 'and w_ws_id = 10' onto the end changes to 30+
> > seconds. Can anyone see why? I've included the explain for the long
> > select.
>
> You really ought to provide EXPLAIN ANALYZE output for both versions if
> you want intelligent commentary --- otherwise we're just guessing.
>
> But I would guess the problem is that the planner is way off about the
>
> number of rows satisfying the joint condition --- it thinks two:
> > -> Index Scan using walon_hide_index on walon
> > (cost=0.00..85.04 rows=2 width=140) Index Cond: (w_hide = 0)
> > Filter: (w_ws_id = 10)
>
> This plan is good if there really are only a couple rows, but degrades
> quickly if there are many...
>
> regards, tom lane

Thanks Tom

I'll bear that in mind in future.

The problem was fixed by running a 'vacuum analyse' so it looks like the
planner was getting confused.

Gary

--
Gary Stainburn

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