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: 2017-11-10T02:31:22Z
Lists: pgsql-hackers 
On Fri, Nov 10, 2017 at 12:05 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Nov 9, 2017 at 12:08 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> This change looks suspicious to me.  I think here we can't use the
>> tupDesc constructed from targetlist.  One problem, I could see is that
>> the check for hasOid setting in tlist_matches_tupdesc won't give the
>> correct answer.   In case of the scan, we use the tuple descriptor
>> stored in relation descriptor which will allow us to take the right
>> decision in tlist_matches_tupdesc.  If you try the statement CREATE
>> TABLE as_select1 AS SELECT * FROM pg_class WHERE relkind = 'r'; in
>> force_parallel_mode=regress, then you can reproduce the problem I am
>> trying to highlight.
>
> I tried this, but nothing seemed to be obviously broken.  Then I
> realized that the CREATE TABLE command wasn't using parallelism, so I
> retried with parallel_setup_cost = 0, parallel_tuple_cost = 0, and
> min_parallel_table_scan_size = 0.  That got it to use parallel query,
> but I still don't see anything broken.  Can you clarify further?
>

Have you set force_parallel_mode=regress; before running the
statement?  If so, then why you need to tune other parallel query
related parameters?

-- 
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.