dbtsai commented on a change in pull request #26085: [SPARK-29434][Core]
Improve the MapStatuses Serialization Performance
URL: https://github.com/apache/spark/pull/26085#discussion_r365022321
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File path: core/src/main/scala/org/apache/spark/MapOutputTracker.scala
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@@ -900,18 +908,42 @@ private[spark] object MapOutputTracker extends Logging {
} {
objOut.close()
}
- val arr = out.toByteArray
+
+ val arr: Array[Byte] = {
+ val zos = new ZstdOutputStream(compressedOut)
+ Utils.tryWithSafeFinally {
+ compressedOut.write(DIRECT)
+ // `out.writeTo(zos)` will write the uncompressed data from `out` to
`zos`
+ // without copying to avoid unnecessary allocation and copy of byte[].
+ out.writeTo(zos)
+ } {
+ zos.close()
+ }
+ compressedOut.toByteArray
+ }
if (arr.length >= minBroadcastSize) {
// Use broadcast instead.
// Important arr(0) is the tag == DIRECT, ignore that while
deserializing !
val bcast = broadcastManager.newBroadcast(arr, isLocal)
// toByteArray creates copy, so we can reuse out
out.reset()
- out.write(BROADCAST)
- val oos = new ObjectOutputStream(new GZIPOutputStream(out))
- oos.writeObject(bcast)
- oos.close()
- val outArr = out.toByteArray
+ val oos = new ObjectOutputStream(out)
+ Utils.tryWithSafeFinally {
+ oos.writeObject(bcast)
+ } {
+ oos.close()
+ }
+ val outArr = {
+ compressedOut.reset()
+ val zos = new ZstdOutputStream(compressedOut)
Review comment:
The actually value of the data (which is already compressed) will not be in
the serialized form of `out.writeTo(zos)` as it's transient. Here, we are just
serializing the reference to the actual data, and the actual data will be
broadcast through `TorrentBroadcast`. See the next log, `"Broadcast mapstatuses
size = " + outArr.length + ", actual size = " + arr.length` for your real data.
The broadcast one is very small.
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