Horton

Re: [POC] Faster processing at Gather node

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Rafia Sabih <rafia.sabih@enterprisedb.com>, PostgreSQL Developers <pgsql-hackers@postgresql.org>
Date: 2017-11-10T04:18:48Z
Lists: pgsql-hackers 
On Fri, Nov 10, 2017 at 8:36 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Nov 9, 2017 at 9:31 PM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> Have you set force_parallel_mode=regress; before running the
>> statement?
>
> Yes, I tried that first.
>
>> If so, then why you need to tune other parallel query
>> related parameters?
>
> Because I couldn't get it to break the other way, I then tried this.
>
> Instead of asking me what I did, can you tell me what I need to do?
> Maybe a self-contained reproducible test case including exactly what
> goes wrong on your end?
>

I think we are missing something very basic because you should see the
failure by executing that statement in force_parallel_mode=regress
even in a freshly created database.  I guess the missing point is that
I am using assertions enabled build and probably you are not (If this
is the reason, then it should have striked me first time).  Anyway, I
am writing steps to reproduce the issue.

1. initdb
2. start server
3. connect using psql
4. set force_parallel_mode=regress;
5. Create Table as_select1 AS SELECT * FROM pg_class WHERE relkind = 'r';


-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

Commits

  1. C comment: fix wording about shared memory message queue

  2. shm_mq: Have the receiver set the sender's less frequently.

  3. shm_mq: Reduce spinlock usage.

  4. Remove use of byte-masking macros in record_image_cmp

  5. Remove memory leak protection from Gather and Gather Merge nodes.

  6. Avoid projecting tuples unnecessarily in Gather and Gather Merge.

  7. Tweak use of ExecContextForcesOids by Gather (Merge).

  8. Pass eflags down to parallel workers.

  9. Disable installcheck tests for test_session_hooks

  10. First-draft release notes for 10.1.

  11. Remove TupleDesc remapping logic from tqueue.c.

  12. Avoid memory leaks when a GatherMerge node is rescanned.

  13. Code review for nodeGatherMerge.c.

  14. Add a Gather Merge executor node.

  15. Push scan/join target list beneath Gather when possible.