Horton

Re: Partition-wise aggregation/grouping

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, David Rowley <david.rowley@2ndquadrant.com>, Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>, Rajkumar Raghuwanshi <rajkumar.raghuwanshi@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-10-28T09:37:36Z
Lists: pgsql-hackers 
On Fri, Oct 27, 2017 at 1:01 PM, Jeevan Chalke
<jeevan.chalke@enterprisedb.com> wrote:
> 1. Added separate patch for costing Append node as discussed up-front in the
> patch-set.
> 2. Since we now cost Append node, we don't need
> partition_wise_agg_cost_factor
> GUC. So removed that. The remaining patch hence merged into main
> implementation
> patch.
> 3. Updated rows in test-cases so that we will get partition-wise plans.

With 0006 applied, cost_merge_append() is now a little bit confused:

    /*
     * Also charge a small amount (arbitrarily set equal to operator cost) per
     * extracted tuple.  We don't charge cpu_tuple_cost because a MergeAppend
     * node doesn't do qual-checking or projection, so it has less overhead
     * than most plan nodes.
     */
    run_cost += cpu_operator_cost * tuples;

    /* Add MergeAppend node overhead like we do it for the Append node */
    run_cost += cpu_tuple_cost * DEFAULT_APPEND_COST_FACTOR * tuples;

The first comment says that we don't add cpu_tuple_cost, and the
second one then adds half of it anyway.

I think it's fine to have a #define for DEFAULT_APPEND_COST_FACTOR,
because as you say it's used twice, but I don't think that should be
exposed in cost.h; I'd make it private to costsize.c and rename it to
something like APPEND_CPU_COST_MULTIPLIER.  The word DEFAULT, in
particular, seems useless to me, since there's no provision for it to
be overridden by a different value.

What testing, if any, can we think about doing with this plan to make
sure it doesn't regress things?  For example, if we do a TPC-H run
with partitioned tables and partition-wise join enabled, will any
plans change with this patch?  Do they get faster or not?  Anyone have
other ideas for what to test?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. postgres_fdw: Push down partition-wise aggregation.

  2. Remove 'target' from GroupPathExtraData.

  3. Implement partition-wise grouping/aggregation.

  4. Don't pass the grouping target around unnecessarily.

  5. Determine grouping strategies in create_grouping_paths.

  6. Defer creation of partially-grouped relation until it's needed.

  7. Split create_grouping_paths into degenerate and non-degenerate cases.

  8. Pass additional arguments to a couple of grouping-related functions.

  9. Fix logic error in add_paths_to_partial_grouping_rel.

  10. Minor cleanup of code related to partially_grouped_rel.

  11. Add a new upper planner relation for partially-aggregated results.

  12. Charge cpu_tuple_cost * 0.5 for Append and MergeAppend nodes.

  13. Rename enable_partition_wise_join to enable_partitionwise_join

  14. Factor some code out of create_grouping_paths.

  15. Pad XLogReaderState's main_data buffer more aggressively.

  16. Prevent int128 from requiring more than MAXALIGN alignment.

  17. Fix DROP SUBSCRIPTION hang

  18. Inject $(ICU_LIBS) regardless of platform.

  19. Some preliminary refactoring towards partitionwise join.