| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: parallel joins, and better parallel explain |
| Date: | 2015-12-23 19:14:35 |
| Message-ID: | CA+Tgmobh3ui-W2YEjXu2hEbi8G9ffmSM4h0nk0rwyvgRY_q8Gw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Dec 23, 2015 at 2:34 AM, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>> I think the gather-reader-order patch will fix this. Here's a test
>> with all three patches.
>
> Yeah right, After applying all three patches this problem is fixed, now
> parallel hash join is faster than normal hash join.
Thanks. I've committed the two smaller patches; it seems fairly clear
that those are good changes independent of the parallel join stuff.
> I have tested one more case which Amit mentioned, I can see in that case
> parallel plan (parallel degree>= 3) is still slow, In Normal case it selects
> "Hash Join" but in case of parallel worker > 3 it selects Parallel "Nest
> Loop Join" which is making it costlier.
Hmm, I'm not sure why that is happening. I'll poke at it a bit.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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