Our job is creating what appears to be an inordinate number of very small
tasks, which blow out our os inode and file limits. Rather than continually
upping those limits, we are seeking to understand whether our real problem
is that too many tasks are running, perhaps because we are mis-configured or
we are coding incorrectly.
Rather than posting our actual code I have re-created the essence of the
matter in the shell with a directory of files simulating the data we deal
with. We have three servers, each with 8G RAM.
Given 1,000 files, each containing a string of 100 characters, in the
myfiles directory:
val data = sc.textFile("/user/foo/myfiles/*")
val c = data.count
The count operation produces 1,000 tasks. Is this normal?
val cart = data.cartesian(data)
cart.count
The cartesian operation produces 1M tasks. I understand that the cartesian
product of 1,000 items against itself is 1M, however, it seems the overhead
of all this task creation and file I/O of all these tiny files outweighs the
gains of distributed computing. What am I missing here?
Below is the truncated output of the count operation, if this helps indicate
a configuration problem.
Thank you.
scala> data.count
14/12/16 07:40:46 INFO FileInputFormat: Total input paths to process : 1000
14/12/16 07:40:47 INFO SparkContext: Starting job: count at <console>:15
14/12/16 07:40:47 INFO DAGScheduler: Got job 0 (count at <console>:15) with
1000 output partitions (allowLocal=false)
14/12/16 07:40:47 INFO DAGScheduler: Final stage: Stage 0(count at
<console>:15)
14/12/16 07:40:47 INFO DAGScheduler: Parents of final stage: List()
14/12/16 07:40:47 INFO DAGScheduler: Missing parents: List()
14/12/16 07:40:47 INFO DAGScheduler: Submitting Stage 0
(/user/ds/randomfiles/* MappedRDD[3] at textFile at <console>:12), which has
no missing parents
14/12/16 07:40:47 INFO MemoryStore: ensureFreeSpace(2400) called with
curMem=507154, maxMem=278019440
14/12/16 07:40:47 INFO MemoryStore: Block broadcast_2 stored as values in
memory (estimated size 2.3 KB, free 264.7 MB)
14/12/16 07:40:47 INFO MemoryStore: ensureFreeSpace(1813) called with
curMem=509554, maxMem=278019440
14/12/16 07:40:47 INFO MemoryStore: Block broadcast_2_piece0 stored as bytes
in memory (estimated size 1813.0 B, free 264.7 MB)
14/12/16 07:40:47 INFO BlockManagerInfo: Added broadcast_2_piece0 in memory
on dev-myserver-1.abc.cloud:44041 (size: 1813.0 B, free: 265.1 MB)
14/12/16 07:40:47 INFO BlockManagerMaster: Updated info of block
broadcast_2_piece0
14/12/16 07:40:47 INFO DAGScheduler: Submitting 1000 missing tasks from
Stage 0 (/user/ds/randomfiles/* MappedRDD[3] at textFile at <console>:12)
14/12/16 07:40:47 INFO TaskSchedulerImpl: Adding task set 0.0 with 1000
tasks
14/12/16 07:40:47 INFO TaskSetManager: Starting task 1.0 in stage 0.0 (TID
0, dev-myserver-2.abc.cloud, NODE_LOCAL, 1202 bytes)
14/12/16 07:40:47 INFO TaskSetManager: Starting task 0.0 in stage 0.0 (TID
1, dev-myserver-3.abc.cloud, NODE_LOCAL, 1201 bytes)
14/12/16 07:40:47 INFO TaskSetManager: Starting task 2.0 in stage 0.0 (TID
2, dev-myserver-1.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:47 INFO TaskSetManager: Starting task 4.0 in stage 0.0 (TID
3, dev-myserver-2.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:47 INFO TaskSetManager: Starting task 3.0 in stage 0.0 (TID
4, dev-myserver-3.abc.cloud, NODE_LOCAL, 1204 bytes)
14/12/16 07:40:47 INFO TaskSetManager: Starting task 5.0 in stage 0.0 (TID
5, dev-myserver-1.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:47 INFO ConnectionManager: Accepted connection from
[dev-myserver-3.abc.cloud/10.40.13.192:36133]
14/12/16 07:40:47 INFO ConnectionManager: Accepted connection from
[dev-myserver-2.abc.cloud/10.40.13.195:35716]
14/12/16 07:40:47 INFO ConnectionManager: Accepted connection from
[dev-myserver-1.abc.cloud/10.40.13.194:33728]
14/12/16 07:40:47 INFO SendingConnection: Initiating connection to
[dev-myserver-1.abc.cloud/10.40.13.194:49458]
14/12/16 07:40:47 INFO SendingConnection: Initiating connection to
[dev-myserver-3.abc.cloud/10.40.13.192:58579]
14/12/16 07:40:47 INFO SendingConnection: Initiating connection to
[dev-myserver-2.abc.cloud/10.40.13.195:52502]
14/12/16 07:40:47 INFO SendingConnection: Connected to
[dev-myserver-3.abc.cloud/10.40.13.192:58579], 1 messages pending
14/12/16 07:40:47 INFO SendingConnection: Connected to
[dev-myserver-1.abc.cloud/10.40.13.194:49458], 1 messages pending
14/12/16 07:40:47 INFO SendingConnection: Connected to
[dev-myserver-2.abc.cloud/10.40.13.195:52502], 1 messages pending
14/12/16 07:40:47 INFO BlockManagerInfo: Added broadcast_2_piece0 in memory
on dev-myserver-1.abc.cloud:49458 (size: 1813.0 B, free: 1060.0 MB)
14/12/16 07:40:47 INFO BlockManagerInfo: Added broadcast_2_piece0 in memory
on dev-myserver-3.abc.cloud:58579 (size: 1813.0 B, free: 1060.0 MB)
14/12/16 07:40:47 INFO BlockManagerInfo: Added broadcast_2_piece0 in memory
on dev-myserver-2.abc.cloud:52502 (size: 1813.0 B, free: 1060.0 MB)
14/12/16 07:40:48 INFO BlockManagerInfo: Added broadcast_1_piece0 in memory
on dev-myserver-3.abc.cloud:58579 (size: 32.5 KB, free: 1060.0 MB)
14/12/16 07:40:48 INFO BlockManagerInfo: Added broadcast_1_piece0 in memory
on dev-myserver-2.abc.cloud:52502 (size: 32.5 KB, free: 1060.0 MB)
14/12/16 07:40:48 INFO BlockManagerInfo: Added broadcast_1_piece0 in memory
on dev-myserver-1.abc.cloud:49458 (size: 32.5 KB, free: 1060.0 MB)
14/12/16 07:40:49 INFO TaskSetManager: Starting task 6.0 in stage 0.0 (TID
6, dev-myserver-1.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:49 INFO TaskSetManager: Starting task 7.0 in stage 0.0 (TID
7, dev-myserver-1.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:49 INFO TaskSetManager: Starting task 19.0 in stage 0.0 (TID
8, dev-myserver-2.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:49 INFO TaskSetManager: Starting task 23.0 in stage 0.0 (TID
9, dev-myserver-2.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:49 INFO TaskSetManager: Starting task 8.0 in stage 0.0 (TID
10, dev-myserver-3.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:49 INFO TaskSetManager: Starting task 9.0 in stage 0.0 (TID
11, dev-myserver-3.abc.cloud, NODE_LOCAL, 1203 bytes)
14/12/16 07:40:49 INFO TaskSetManager: Finished task 2.0 in stage 0.0 (TID
2) in 1964 ms on dev-myserver-1.abc.cloud (1/1000)
14/12/16 07:40:49 INFO TaskSetManager: Finished task 1.0 in stage 0.0 (TID
0) in 2000 ms on dev-myserver-2.abc.cloud (2/1000)
14/12/16 07:40:49 INFO TaskSetManager: Finished task 5.0 in stage 0.0 (TID
5) in 1975 ms on dev-myserver-1.abc.cloud (3/1000)
....
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