Github user viper-kun commented on a diff in the pull request:
https://github.com/apache/spark/pull/11886#discussion_r57102821
--- Diff: core/src/main/scala/org/apache/spark/MapOutputTracker.scala ---
@@ -443,13 +443,12 @@ private[spark] class MapOutputTrackerMaster(conf:
SparkConf)
statuses = mapStatuses.getOrElse(shuffleId, Array[MapStatus]())
epochGotten = epoch
}
- }
- // If we got here, we failed to find the serialized locations in the
cache, so we pulled
- // out a snapshot of the locations as "statuses"; let's serialize and
return that
- val bytes = MapOutputTracker.serializeMapStatuses(statuses)
- logInfo("Size of output statuses for shuffle %d is %d
bytes".format(shuffleId, bytes.length))
- // Add them into the table only if the epoch hasn't changed while we
were working
- epochLock.synchronized {
+
+ // If we got here, we failed to find the serialized locations in the
cache, so we pulled
--- End diff --
The problem description:
Execute the query listed in
jira(https://issues.apache.org/jira/browse/SPARK-14065), all tasks running on
some executor are slow.
Slow executor logs show that RPC(GetMapOutputStatuses) get
RpcTimeoutException
```
Error sending message [message = GetMapOutputStatuses(1)] in 1 attempts |
org.apache.spark.Logging$class.logWarning(Logging.scala:92)
org.apache.spark.rpc.RpcTimeoutException: Futures timed out after [120
seconds]. This timeout is controlled by spark.network.timeout
```
Driver logs shows that serialize mapstatus is slow
```
16/03/22 11:47:07 INFO [dispatcher-event-loop-36] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:47:14 INFO [dispatcher-event-loop-30] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:47:21 INFO [dispatcher-event-loop-3] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:47:27 INFO [dispatcher-event-loop-32] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:47:34 INFO [dispatcher-event-loop-31] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:47:41 INFO [dispatcher-event-loop-38] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:47:47 INFO [dispatcher-event-loop-4] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:47:54 INFO [dispatcher-event-loop-37] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
16/03/22 11:48:00 INFO [dispatcher-event-loop-28] MapOutputTrackerMaster:
Size of output statuses for shuffle 1 is 10298063 bytes
```
When reduce task start, all executors will get mapstatus from
driver.Because "MapOutputTracker.serializeMapStatuses(statuses)" is out of
epochLock.synchronized {}
,all thread will do the operation -
MapOutputTracker.serializeMapStatuses(statuses). In function
serializeMapStatuses, it has sync on statuses. So Serialize is one by one.
Every serialize cost 7 seconds. We have 80 executors, it total cost 560
seconds. The result is some executor get mapstatus timeout.
This patch put "MapOutputTracker.serializeMapStatuses(statuses)" into
epochLock.synchronized {}, it will increase probability of using cached
serialized status.
I have test listed sql in 30T tpcds. The result shows it faster than old.
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