Horton

Re: speeding up planning with partitions

Amit Langote <langote_amit_f8@lab.ntt.co.jp>

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From: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
To: "Imai, Yoshikazu" <imai.yoshikazu@jp.fujitsu.com>
Cc: David Rowley <david.rowley@2ndquadrant.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2019-01-17T10:24:47Z
Lists: pgsql-hackers 
Thank you Imai-san for testing.  Sorry it totally slipped my mind to reply
to this email.

On 2019/01/09 11:08, Imai, Yoshikazu wrote:
> I wonder why force_custom_plan is faster than auto after applied the patch.
> 
> When we use PREPARE-EXECUTE, a generic plan is created and used if its cost is
> cheaper than creating and using a custom plan with plan_cache_mode='auto',
> while a custom plan is always created and used with plan_cache_mode='force_custom_plan'.
> So one can think the difference in above results is because of creating or
> using a generic plan.
> 
> I checked how many times a generic plan is created during executing pgbench and
> found a generic plan is created only once and custom plans are created at other
> times with plan_cache_mode='auto'. I also checked the time of creating a
> generic plan, but it didn't take so much(250ms or so with 4096 partitions). So
> the time of creating a generic plan does not affect the performance.
> 
> Currently, a generic plan is created at sixth time of executing EXECUTE query.
> I changed it to more later (ex. at 400,000th time of executing EXECUTE query on
> master with 4096 partitions, because 7000TPS x 60sec=420,0000 transactions are
> run while executing pgbench.), then there are almost no difference between auto
> and force_custom_plan. I think that creation of a generic plan affects the time
> of executing queries which are ordered after creating generic plan.
> 
> If my assumption is right, we can expect some additional process is occurred at
> executing queries ordered after creating a generic plan, which results in auto is
> slower than force_custom_plan because of additional process. But looking at
> above results, on master with 4096 partitions, auto is faster than force_custom_plan.
> So now I am confused.
> 
> Do you have any ideas what does affect the performance?

Are you saying that, when using auto mode, all executions of the query
starting from 7th are slower than the first 5 executions?  That is, the
latency of creating and using a custom plan increases *after* a generic
plan is created and discarded on the 6th execution of the query?  If so,
that is inexplicable to me.

Thanks,
Amit

Commits

  1. Clean up handling of constraint_exclusion and enable_partition_pruning.

  2. Add test case exercising formerly-unreached code in inheritance_planner.

  3. Speed up planning when partitions can be pruned at plan time.

  4. Avoid crash in partitionwise join planning under GEQO.

  5. Avoid passing query tlist around separately from root->processed_tlist.

  6. Build "other rels" of appendrel baserels in a separate step.

  7. Get rid of duplicate child RTE for a partitioned table.

  8. Rearrange make_partitionedrel_pruneinfo to avoid work when we can't prune.

  9. Don't copy PartitionBoundInfo in set_relation_partition_info.

  10. Move building of child base quals out into a new function

  11. Reorganize planner code moved in b60c39759908

  12. Move inheritance expansion code into its own file

  13. Fix inherited UPDATE/DELETE with UNION ALL subqueries.

  14. Rearrange planner to save the whole PlannerInfo (subroot) for a subquery.