| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
| Cc: | Oleg Bartunov <obartunov(at)gmail(dot)com>, Ildar Musin <i(dot)musin(at)postgrespro(dot)ru>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Index Onlys Scan for expressions |
| Date: | 2016-08-23 16:56:49 |
| Message-ID: | CA+TgmoboALURw6MWmoAwoneX=3mwe=FwbrZAmqLbCbf=w9VjmA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Aug 16, 2016 at 2:43 AM, Alexander Korotkov
<a(dot)korotkov(at)postgrespro(dot)ru> wrote:g of pg_operator.oprassociative...
> Another problem is computational complexity of such transformations. AFAIR,
> few patches for making optimizer smarter with expressions were already
> rejected because of this reason.
s/few/many/
> Also, even if we would have such transformation of expressions, floating
> points types would be still problematic, because (a + b) + c = a + (b + c)
> is not exactly true for them because of computational error.
Right. I think matching expressions exactly is plenty good enough.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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