| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>, Rafia Sabih <rafia(dot)sabih(at)enterprisedb(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Parallel Append implementation |
| Date: | 2017-09-29 22:32:29 |
| Message-ID: | CA+TgmoYo+F2zTQ_4vCYcBenjoORxnhrf0eqa4oaNkGHkqD=Uyg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Sep 29, 2017 at 7:48 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> I think in general the non-partial paths should be cheaper as compared
> to partial paths as that is the reason planner choose not to make a
> partial plan at first place. I think the idea patch is using will help
> because the leader will choose to execute partial path in most cases
> (when there is a mix of partial and non-partial paths) and for that
> case, the leader is not bound to complete the execution of that path.
> However, if all the paths are non-partial, then I am not sure much
> difference it would be to choose one path over other.
The case where all plans are non-partial is the case where it matters
most! If the leader is going to take a share of the work, we want it
to take the smallest share possible.
It's a lot fuzzier what is best when there are only partial plans.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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