Hi!
I have finally added support for Partial IndexAggregate. There was a problem with
sortgroupref and target list entries mismatch due to partial aggregates in it.
To solve this I had to add new argument to 'create_agg_path' - 'pathkeys' which is
a List of PathKey.
Previously this information was calculated in the function just like AGG_SORTED
do this. But when we calculating pathkeys we must consider whether it is a child
rel to properly build pathkeys and if so use it's parent. The latter information is
not known inside 'create_agg_path', thus instead of passing 'parent' we explicitly
pass already built 'pathkeys'. I did not change AGG_SORTED logic, so this is used
only by AGG_INDEX.
This logic is placed in another patch file just to make review of this change easier.
Also, cost calculation logic is adjusted a bit - it takes into account top-down index
traversal and final external merge cost is added only if spill expected.
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Sergey Soloviev
TantorLabs: https://tantorlabs.com
