| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Jim Nasby <jim(at)nasby(dot)net> |
| Cc: | Mathieu De Zutter <mathieu(at)dezutter(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Merlin Moncure <mmoncure(at)gmail(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: NULLS LAST performance |
| Date: | 2011-03-10 15:55:16 |
| Message-ID: | AANLkTikqMnwmbQ+Hm5c3O4c9NzjbKJUpAx_1ObutbwGE@mail.gmail.com |
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| Lists: | pgsql-performance |
On Wed, Mar 9, 2011 at 6:01 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
> Unfortunately, I don't think the planner actually has that level of knowledge.
Actually, I don't think it would be that hard to teach the planner
about that special case...
> A more reasonable fix might be to teach the executor that it can do 2 scans of the index: one to get non-null data and a second to get null data. I don't know if the use case is prevalent enough to warrant the extra code though.
That would probably be harder, but useful. I thought about working on
it before but got sidetracked onto other things.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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