yikf opened a new pull request, #13115:
URL: https://github.com/apache/gluten/pull/13115
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## What changes are proposed in this pull request?
The parallel broadcast hash-table build path (numThreads > 1 in
HashJoinBuilder.nativeBuild) dispatched its CPU-bound build tasks onto
VeloxBackend::ioExecutor(). That executor is reserved for async IO tasks (split
preloading, DirectBufferedInput).
```cpp
// FIXME: This reuses the io executor which is supposed to only serve async
IO tasks.
auto executor = VeloxBackend::get()->ioExecutor();
Running CPU-heavy hash-table build work on the IO pool makes it contend with
genuine IO work on the same threads.
```
This PR introduces a dedicated, lazily-created CPU thread pool
(VeloxBackend::hashTableBuildExecutor()), following the existing
getReaderThreadPool() std::call_once pattern, and switches both places that
previously reused the io executor:
1. the parallel build task dispatch (folly::via(executor, ...)), and
2. the parallel join-table merge passed to prepareJoinTable(...).
The pool size is controlled by a new native config key
spark.gluten.sql.columnar.backend.velox.hashTableBuildThreads. A value <= 0
(the default) falls back to kNumTaskSlotsPerExecutor, i.e. the same sizing this
path previously inherited from the io executor. So default behavior is
unchanged — this is a pool-isolation change, not a concurrency change. The key
is native-only and passed through via the
spark.gluten.sql.columnar.backend.velox. prefix, mirroring how spillThreadNum
is handled.
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## How was this patch tested?
GA.
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Generated-by: Claude claude-opus-4-8
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