mirror of https://github.com/apache/druid.git
529b983ad0
* GroupBy: Reduce allocations by reusing entry and key holders. Two main changes: 1) Reuse Entry objects returned by various implementations of Grouper.iterator. 2) Reuse key objects contained within those Entry objects. This is allowed by the contract, which states that entries must be processed and immediately discarded. However, not all call sites respected this, so this patch also updates those call sites. One particularly sneaky way that the old code retained entries too long is due to Guava's MergingIterator and CombiningIterator. Internally, these both advance to the next value prior to returning the current value. So, this patch addresses that in two ways: 1) For merging, we have our own implementation MergeIterator already, although it had the same problem. So, this patch updates our implementation to return the current item prior to advancing to the next item. It also adds a forbidden-api entry to ensure that this safer implementation is used instead of Guava's. 2) For combining, we address the problem in a different way: by copying the key when creating the new, combined entry. * Attempt to fix test. * Remove unused import. |
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