Re: Why does the number of rows are different in actual and estimated.

On Thu, Dec 13, 2012 at 8:50 PM, Evgeny Shishkin <itparanoia@gmail.com> wrote:
>>> OP joins 8 tables, and i suppose join collapse limit is set to default 8. I thought postgresql's optimiser is not
mysql's.
>>
>> It's not obvious to me that there's anything very wrong with the plan.
>> An 8-way join that produces 150K rows is unlikely to run in milliseconds
>> no matter what the plan.  The planner would possibly have done the last
>> join step differently if it had had a better rowcount estimate, but even
>> if that were free the query would still have been 7 seconds (vs 8.5).
>>
>
> May be in this case it is. I once wrote to this list regarding similar problem - joining 4 tables, result set are off
by2257 times - 750ms vs less then 1ms. Unfortunately the question was not accepted to the list. 
>
> I spoke to Bruce Momjian about that problem on one local conference, he said shit happens :)

I think it's more likely a missing FK constraint.