[feat][cp] Add merge source start processing mechanism for pyspark-velox#405
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Summary: Corresponding PR: facebookincubator/velox#13139 Extend MergeSource to support merge source start control mechanism used to implement lazy source start to cap the local merge source memory usage. The merge operator needs to call start on each MergeSource to signal producer the start of source processing. Each source producer, CallbackSink operator check if the corresponding merge source is started or not in isBlocked method. The exchange the source start signal is expected to happen once. Unit test is added to verify this behavior. This PR also move the producer/consumer signal out of locks to prevent potential deadlock plus some code cleanup in the relevant code path. The followup is to add recursive spill based on the lazy start mechanism built to cap the merge source memory usage when there are a large number of sources such in pyspark-velox use case.
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What problem does this PR solve?
Issue Number: close #191
Type of Change
Description
Summary:
Extend MergeSource to support merge source start control mechanism used to implement lazy source start to cap the local merge source memory usage. The merge operator needs to call start on each MergeSource to signal producer the start of source processing. Each source producer, CallbackSink operator check if the corresponding merge source is started or not in isBlocked method. The exchange the source start signal is expected to happen once. Unit test is added to verify this behavior. This PR also move the producer/consumer signal out of locks to prevent potential deadlock plus some code cleanup in the relevant code path.
The followup is to add recursive spill based on the lazy start mechanism built to cap the merge source memory usage when there are a large number of sources such in pyspark-velox use case.
Performance Impact
No Impact: This change does not affect the critical path (e.g., build system, doc, error handling).
Positive Impact: I have run benchmarks.
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Negative Impact: Explained below (e.g., trade-off for correctness).
Release Note
Please describe the changes in this PR
Release Note:
Checklist (For Author)
Breaking Changes
No
Yes (Description: ...)
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