Horton

Re: Partition-wise aggregation/grouping

Antonin Houska <ah@cybertec.at>

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From: Antonin Houska <ah@cybertec.at>
To: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
Cc: pgsql-hackers@postgresql.org
Date: 2017-04-05T08:30:57Z
Lists: pgsql-hackers 
The promised new version of my patch is here:

https://www.postgresql.org/message-id/9666.1491295317%40localhost

Jeevan Chalke <jeevan.chalke@enterprisedb.com> wrote:

> On Tue, Mar 21, 2017 at 1:47 PM, Antonin Houska <ah@cybertec.at> wrote:
> 
>  Jeevan Chalke <jeevan.chalke@enterprisedb.com> wrote:
> 
> IIUC, it seems that you are trying to push down the aggregation into the
> joining relations. So basically you are converting
> Agg -> Join -> {scan1, scan2} into
> FinalAgg -> Join -> {PartialAgg -> scan1, PartialAgg -> scan2}.
> In addition to that your patch pushes aggregates on base rel to its children,
> if any.
> 
> Where as what I propose here is pushing down aggregation below the append
> node keeping join/scan as is. So basically I am converting
> Agg -> Append-> Join -> {scan1, scan2} into
> Append -> Agg -> Join -> {scan1, scan2}.
> This will require partition-wise join as posted in [1].
> But I am planning to make this work for partitioned relations and not for
> generic inheritance.
> 
> I treat these two as separate strategies/paths to be consider while planning.
> 
> Our work will overlap when we are pushing down the aggregate on partitioned
> base relation to its children/partitions.
> 
> I think you should continue working on pushing down aggregate onto the
> joins/scans where as I will continue my work on pushing down aggregates to
> partitions (joins as well as single table). Once we are done with these task,
> then we may need to find a way to integrate them.
> 
> [1] https://www.postgresql.org/message-id/flat/CAFjFpRfQ8GrQvzp3jA2wnLqrHmaXna-urjm_UY9BqXj=EaDTSA@mail.gmail.com#CAFjFpRfQ8GrQvzp3jA2wnLqrHmaXna-urjm_UY9BqXj=EaDTSA@mail.gmail.com

My patch does also create (partial) aggregation paths below the Append node,
but only expects SeqScan as input. Please check if you patch can be based on
this or if there's any conflict.

(I'll probably be unable to respond before Monday 04/17.)

-- 
Antonin Houska
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de, http://www.cybertec.at

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.