| From: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-bugs <pgsql-bugs(at)postgresql(dot)org> |
| Subject: | Re: Introducing floating point cast into filter drastically changes row estimate |
| Date: | 2012-10-24 20:51:56 |
| Message-ID: | CAHyXU0yLQpshj5mgF_2zzjyKqmrniMqhzrbpBd7SZ1MD2UO=dQ@mail.gmail.com |
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| Lists: | pgsql-bugs |
On Wed, Oct 24, 2012 at 3:33 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
>> Yeah -- I have a case where a large number of joins are happening that
>> have a lot of filtering based on expressions and things like that.
>
> Might be worth your while to install some indexes on those expressions,
> if only to trigger collection of stats about them.
Not practical -- these expressions are all about 'outlier culling'.
It's just wasteful to materialize indexes for stastical purposes only.
Anyways, in this case, I just refactored the query into a CTE.
Hm -- what if you could flag a table dependent expression for being
interesting for statistics? Or what about planner hints for boolean
expressions (ducks) ... 'likely(boolexpr)'?
merlin
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