Dandandan opened a new pull request, #19773:
URL: https://github.com/apache/datafusion/pull/19773
This commit optimizes the `CollectLeft` execution mode in `HashJoinExec` by
parallelizing the build-side processing. Previously, `CollectLeft` required the
build side to be coalesced into a single partition, creating a performance
bottleneck.
This optimization removes the single-partition requirement and introduces a
new `collect_left_input_parallel` function. This function executes all
build-side partitions concurrently, collects their batches, and then populates
a shared hash map in parallel using a mutex for synchronization.
This change avoids the need for an explicit `CoalescePartitions` operator
upstream and leverages available parallelism to significantly speed up the hash
join build phase for `CollectLeft` scenarios.
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