From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Rafia Sabih <rafia(dot)sabih(at)enterprisedb(dot)com>, Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Partition-wise join for join between (declaratively) partitioned tables |
Date: | 2017-04-26 16:43:27 |
Message-ID: | CA+TgmoYCBaUD6d=bOt8G1j-u9OZXQHB99xqRdJ8dUYzBE2ufbA@mail.gmail.com |
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On Wed, Apr 26, 2017 at 12:41 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> So this is about a cross-type join,
>> not multiple types within a single partitioning hierarchy, as you
>> might also gather from the subject line of this thread.
>
> OK, but I still don't understand why any type conversion is needed
> in such a case. The existing join estimators don't try to do that,
> for the good and sufficient reasons you and I have already mentioned.
> They just apply the given cross-type join operator, and whatever
> cross-type selectivity estimator might be associated with it, and
> possibly other cross-type operators obtained from the same btree
> opfamily.
>
> The minute you get into trying to do any type conversion that is not
> mandated by the semantics of the query as written, you're going to
> have problems.
There is no daylight whatsoever between us on this issue.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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