Re: Weird query plan

Tom Lane wrote:

>Dmitry Tkach <dmitry@openratings.com> writes:
>
>
>>Also, I have another copy (not exact copy, but identical schema, and
>>similar content... but about twice smaller) of the original database...
>>I tried my query on it, and it works right too.
>>
>>
>
>
>
>>So, there must be something wrong with that particular database I suppose...
>>
>>
>
>Hmm.  Take a look at the pg_stats statistics for the id columns in each
>case.  Could the ones for the misbehaving tables be out of whack
>somehow?  I'm wondering for example if the planner discounted the >=
>condition because it thought it would match all the rows.
>
>
>
Well... It *does* match (almost) all the rows (there are about a million
rows before that key, and the remaining 79 mil after)...
The stats look in synch with that:

for a:
stavalues1  |
{1000488,33495482,69111011,99286820,129611281,204441828,331968789,508451171,782660252,869480434,989787700}
for b:
stavalues1  |
{1008692,54892364,110119463,192551141,300490851,389609207,465139533,570442801,706876547,849087358,989851076}

(The key in the criteria was 7901288 - somewhere in the first bucket)


*But* isn't  my 'limit' clause supposed to affect that decision? I mean,
even though the filter isn't very selective, it should still speed up
getting the *first* match...


Thanks!

Dima

P.S. I also tried to look at the stats of that other database I
mentioned... The stats for b look similar:
stavalues1  |
{1028104,25100079,50685614,78032989,105221902,135832793,199827486,611968165,807597786,884897604,969971779}

But the stats for a are just *not there at all* (is it even possible?)
Could it be the reason why it works on that database (because it uses
the default stats instead of the real thing)?