GroupPathExtraData now completely absorbs members from and replaces OtherUpperPathExtraData. This means that we have to consider a way to pass GroupPathExtraData to FDWs through GetForeignUpperPaths(). I haven't tried it in this patch.
Initially, I was passing OtherUpperPathExtraData to FDW. But now we need to pass GroupPathExtraData.
However, since GetForeignUpperPaths() is a generic function for all upper relations, we might think of renaming this struct to UpperPathExtraData. Add an UpperRelationKind member to it
Which will be used to distinguish the passed in extra data. But now we only have extra data for grouping only, I chose not to do that here. But someone, when needed, may choose this approach.
With this patch there's a failure in partition_aggregation where the patch is creating paths with MergeAppend with GatherMerge underneath. I think this is related to the call add_paths_to_partial_grouping_rel() when try_parallel_aggregation is true. But I didn't investigate it further.
I fixed it. We need to pass is_partial_agg instead of extra->partial_partitionwise_grouping while calling add_paths_to_partial_grouping_rel() in case of parallelism.
With those two things remaining I am posting this patch, so that Jeevan Chalke can merge this patch into his patches and also merge some of his changes related to mine and Robert's changes. Let me know if this refactoring looks good.
Will rebase my changes tomorrow.
-- Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
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Jeevan Chalke Technical Architect, Product Development EnterpriseDB Corporation The Enterprise PostgreSQL Company