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author | Josh Rosen <joshrosen@databricks.com> | 2015-10-07 13:19:49 -0700 |
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committer | Yin Huai <yhuai@databricks.com> | 2015-10-07 13:19:49 -0700 |
commit | a9ecd06149df4ccafd3927c35f63b9f03f170ae5 (patch) | |
tree | 99d41c5b5f8cd786e2c161c339373a740b4048eb /tags | |
parent | 5be5d247440d6346d667c4b3d817666126f62906 (diff) | |
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[SPARK-10941] [SQL] Refactor AggregateFunction2 and AlgebraicAggregate interfaces to improve code clarity
This patch refactors several of the Aggregate2 interfaces in order to improve code clarity.
The biggest change is a refactoring of the `AggregateFunction2` class hierarchy. In the old code, we had a class named `AlgebraicAggregate` that inherited from `AggregateFunction2`, added a new set of methods, then banned the use of the inherited methods. I found this to be fairly confusing because.
If you look carefully at the existing code, you'll see that subclasses of `AggregateFunction2` fall into two disjoint categories: imperative aggregation functions which directly extended `AggregateFunction2` and declarative, expression-based aggregate functions which extended `AlgebraicAggregate`. In order to make this more explicit, this patch refactors things so that `AggregateFunction2` is a sealed abstract class with two subclasses, `ImperativeAggregateFunction` and `ExpressionAggregateFunction`. The superclass, `AggregateFunction2`, now only contains methods and fields that are common to both subclasses.
After making this change, I updated the various AggregationIterator classes to comply with this new naming scheme. I also performed several small renamings in the aggregate interfaces themselves in order to improve clarity and rewrote or expanded a number of comments.
Author: Josh Rosen <joshrosen@databricks.com>
Closes #8973 from JoshRosen/tungsten-agg-comments.
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