mbutrovich commented on code in PR #3703:
URL: https://github.com/apache/datafusion-comet/pull/3703#discussion_r2942843194
##########
common/src/main/scala/org/apache/spark/sql/comet/util/Utils.scala:
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@@ -252,6 +255,101 @@ object Utils extends CometTypeShim {
new ArrowReaderIterator(Channels.newChannel(ins), source)
}
+ /**
+ * Coalesces many small ChunkedByteBuffers (one per source partition) into a
single
+ * ChunkedByteBuffer. Without coalescing, each consumer task in a broadcast
hash join
+ * deserializes N separate Arrow IPC streams (one per source partition),
which dominates
+ * build-side time when partition counts are high (e.g. 200+ partitions in
TPC-H Q18).
+ *
+ * We decode and append all source batches into one VectorSchemaRoot on the
driver, then
+ * re-serialize once via ArrowStreamWriter. This is done on the driver (not
per-task) so the
+ * cost is paid once rather than once per consumer partition.
+ */
+ def coalesceBroadcastBatches(
+ input: Iterator[ChunkedByteBuffer]): (Array[ChunkedByteBuffer], Long,
Long) = {
+ val buffers = input.filterNot(_.size == 0).toArray
+ if (buffers.isEmpty) {
+ return (Array.empty, 0L, 0L)
+ }
+
+ val allocator = org.apache.comet.CometArrowAllocator
+ .newChildAllocator("broadcast-coalesce", 0, Long.MaxValue)
+ try {
+ var targetRoot: VectorSchemaRoot = null
+ var totalRows = 0L
+ var batchCount = 0
+
+ try {
+ for (bytes <- buffers) {
+ val codec = CompressionCodec.createCodec(SparkEnv.get.conf)
Review Comment:
Yeah I can probably hoist that out. To be honest, I'm not even sure it's
worth compressing the <10MB broadcast, but maybe best to leave it.
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