> > if that index is causing the problem, you may want to consider
setting
> > up partial index to exclude null values.
>
> This is a single column index. I assumed that null column values were
> not indexed. Is my assumption incorrect?
>
> -K
It turns out it is, or it certainly seems to be. I didn't know that :).
So partial index will probably not help for null exclusion...
would be interesting to see if you are getting swaps (check pg_tmp) when
performance breaks down. That is an easy fix, bump work_mem.
Merlin