Apache spark message understanding - scala

Question

Request help to understand this message..
INFO spark.MapOutputTrackerMaster: Size of output statuses for shuffle 2 is **2202921** bytes
what does 2202921 mean here?
My job does a shuffle operation and while reading shuffle files from previous stage, it gives the message first and then after sometime it fails with below error:
14/11/12 11:09:46 WARN scheduler.TaskSetManager: Lost task 224.0 in stage 4.0 (TID 13938, ip-xx-xxx-xxx-xx.ec2.internal): FetchFailed(BlockManagerId(11, ip-xx-xxx-xxx-xx.ec2.internal, 48073, 0), shuffleId=2, mapId=7468, reduceId=224)
14/11/12 11:09:46 INFO scheduler.DAGScheduler: Marking Stage 4 (coalesce at <console>:49) as failed due to a fetch failure from Stage 3 (map at <console>:42)
14/11/12 11:09:46 INFO scheduler.DAGScheduler: Stage 4 (coalesce at <console>:49) failed in 213.446 s
14/11/12 11:09:46 INFO scheduler.DAGScheduler: Resubmitting Stage 3 (map at <console>:42) and Stage 4 (coalesce at <console>:49) due to fetch failure
14/11/12 11:09:46 INFO scheduler.DAGScheduler: Executor lost: 11 (epoch 2)
14/11/12 11:09:46 INFO storage.BlockManagerMasterActor: Trying to remove executor 11 from BlockManagerMaster.
14/11/12 11:09:46 INFO storage.BlockManagerMaster: Removed 11 successfully in removeExecutor
14/11/12 11:09:46 INFO scheduler.Stage: Stage 3 is now unavailable on executor 11 (11893/12836, false)
14/11/12 11:09:46 INFO scheduler.DAGScheduler: Resubmitting failed stages
14/11/12 11:09:46 INFO scheduler.DAGScheduler: Submitting Stage 3 (MappedRDD[13] at map at <console>:42), which has no missing parents
14/11/12 11:09:46 INFO storage.MemoryStore: ensureFreeSpace(25472) called with curMem=474762, maxMem=11113699737
14/11/12 11:09:46 INFO storage.MemoryStore: Block broadcast_6 stored as values in memory (estimated size 24.9 KB, free 10.3 GB)
14/11/12 11:09:46 INFO storage.MemoryStore: ensureFreeSpace(5160) called with curMem=500234, maxMem=11113699737
14/11/12 11:09:46 INFO storage.MemoryStore: Block broadcast_6_piece0 stored as bytes in memory (estimated size 5.0 KB, free 10.3 GB)
14/11/12 11:09:46 INFO storage.BlockManagerInfo: Added broadcast_6_piece0 in memory on ip-xx.ec2.internal:35571 (size: 5.0 KB, free: 10.4 GB)
14/11/12 11:09:46 INFO storage.BlockManagerMaster: Updated info of block broadcast_6_piece0
14/11/12 11:09:46 INFO scheduler.DAGScheduler: Submitting 943 missing tasks from Stage 3 (MappedRDD[13] at map at <console>:42)
14/11/12 11:09:46 INFO cluster.YarnClientClusterScheduler: Adding task set 3.1 with 943 tasks
My code looks like this,
(rdd1 ++ rdd2).map { t => ((t.id), t) }.groupByKey(1280).map {
case ((id), sequence) =>
val newrecord = sequence.maxBy {
case Fact(id, key, type, day, group, c_key, s_key, plan_id,size,
is_mom, customer_shipment_id, customer_shipment_item_id, asin, company_key, product_line_key, dw_last_updated, measures) => dw_last_updated.toLong
}
((PARTITION_KEY + "=" + newrecord.day.toString + "/part"), (newrecord))
}.coalesce(2048,true).saveAsTextFile("s3://myfolder/PT/test20nodes/")```
I derived 1280 as I have 20 nodes each having 32 cores. I derived it like 2*32*20.

Answer 1

For a Shuffle stage, it will create some ShuffleMapTasks which output the intermediate results to the disk. The location information will be stored in MapStatuses and sent to the MapOutputTrackerMaster(the driver).
Then when the next stage starts to run, it needs these location statuses. So executors will ask MapOutputTrackerMaster to fetch them. MapOutputTrackerMaster will serialize these status to bytes and send them to executors. Here is the size of these status in bytes.
These status will be sent via Akka. And Akka has a limitation to the max message size. You can set it via spark.akka.frameSize:
Maximum message size to allow in "control plane" communication (for serialized tasks and task results), in MB. Increase this if your tasks need to send back large results to the driver (e.g. using collect() on a large dataset).
If the size is greater than spark.akka.frameSize, Akka will refuse to deliver the message and your job will fail. Therefore it can help you adjust spark.akka.frameSize to a best one.