Re: Performance of subselects

Tom Lane wrote:
> No, they're not the same; NOT IN has different semantics for nulls.
>
But in this case the column in the subselect has a not-null constraint.
Does the planner recognize this constraint?
> You're probably at the threshold where it doesn't think the hashtable
> would fit in work_mem.
>
I have read in the docs that the "work_mem" value should be increased
carefully because the total memory used can be many times the value of
"work_mem". Is there any statistics available about how many concurrent
sort or hash operations are running and how much memory they consume?
This would help to find out if the value can be changed without running
out of memory.

Regards,
Christian Schröder

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