[TEZ-2358] Pipelined Shuffle: MergeManager assumptions about 1 merge per source-task

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 0.7.0
• Fix Version/s: 0.7.0
• Target Version/s: 0.7.0
• Hadoop Flags: Reviewed
• Assignee: Rajesh Balamohan
• Reporter: Gopal Vijayaraghavan
• Created: 23/Apr/15 12:10
• Updated: 30/Jun/15 04:53
• Resolved: 27/Apr/15 21:55

Description

The Tez MergeManager code assumes that the src-task-id is unique between merge operations, this results in some confusion when two merge sequences have to process output from the same src-task-id.

private TezRawKeyValueIterator finalMerge(Configuration job, FileSystem fs,
                                       List<MapOutput> inMemoryMapOutputs,
                                       List<FileChunk> onDiskMapOutputs
...
 if (inMemoryMapOutputs.size() > 0) {
      int srcTaskId = inMemoryMapOutputs.get(0).getAttemptIdentifier().getInputIdentifier().getInputIndex();
...
       // must spill to disk, but can't retain in-mem for intermediate merge
        final Path outputPath = 
          mapOutputFile.getInputFileForWrite(srcTaskId,
                                             inMemToDiskBytes).suffix(
                                                 Constants.MERGED_OUTPUT_PREFIX);
...

This or some scenario related to this, results in the following FileChunks list which contains identical named paths with different lengths.

2015-04-23 03:28:50,983 INFO [MemtoDiskMerger [Map_1]] orderedgrouped.MergeManager: Initiating in-memory merge with 6 segments...
2015-04-23 03:28:50,987 INFO [MemtoDiskMerger [Map_1]] impl.TezMerger: Merging 6 sorted segments
2015-04-23 03:28:50,988 INFO [MemtoDiskMerger [Map_1]] impl.TezMerger: Down to the last merge-pass, with 6 segments left of total size: 1165944755 bytes
2015-04-23 03:28:58,495 INFO [MemtoDiskMerger [Map_1]] orderedgrouped.MergeManager: attempt_1429683757595_0141_1_01_000143_0_10027 Merge of the 6 files in-memory complete. Local file is /grid/5/cluster/yarn/local/usercache/gopal/appcache/application_1429683757595_0141/attempt_1429683757595_0141_1_01_000143_0_10027_spill_404.out.merged of size 785583965
2015-04-23 03:28:58,496 INFO [ShuffleAndMergeRunner [Map_1]] orderedgrouped.MergeManager: finalMerge called with 0 in-memory map-outputs and 5 on-disk map-outputs
2015-04-23 03:28:58,496 INFO [ShuffleAndMergeRunner [Map_1]] orderedgrouped.MergeManager: GOPAL: onDiskBytes = 365232290 += 365232290for/grid/4/cluster/yarn/local/usercache/gopal/appcache/application_1429683757595_0141/attempt_1429683757595_0141_1_01_000143_0_10027_spill_1023.out
2015-04-23 03:28:58,496 INFO [ShuffleAndMergeRunner [Map_1]] orderedgrouped.MergeManager: GOPAL: onDiskBytes = 730529899 += 365297609for/grid/5/cluster/yarn/local/usercache/gopal/appcache/application_1429683757595_0141/attempt_1429683757595_0141_1_01_000143_0_10027_spill_404.out
2015-04-23 03:28:58,496 INFO [ShuffleAndMergeRunner [Map_1]] orderedgrouped.MergeManager: GOPAL: onDiskBytes = 1095828683 += 365298784for/grid/5/cluster/yarn/local/usercache/gopal/appcache/application_1429683757595_0141/attempt_1429683757595_0141_1_01_000143_0_10027_spill_404.out

The multiple instances of 404.out indicates that we pulled two pipelined chunks of the same shuffle src id, once into memory and twice onto disk.

2015-04-23 03:28:08,256 INFO [TezTaskEventRouter[attempt_1429683757595_0141_1_01_000143_0]] orderedgrouped.ShuffleInputEventHandlerOrderedGrouped: DME srcIdx: 143, targetIdx: 404, attemptNum: 0, payload: [hasEmptyPartitions: true, host: cn047-10.l42scl.hortonworks.com, port: 13562, pathComponent: attempt_1429683757595_0141_1_00_000404_0_10009_0, runDuration: 0]
2015-04-23 03:28:08,270 INFO [TezTaskEventRouter[attempt_1429683757595_0141_1_01_000143_0]] orderedgrouped.ShuffleInputEventHandlerOrderedGrouped: DME srcIdx: 143, targetIdx: 404, attemptNum: 0, payload: [hasEmptyPartitions: true, host: cn047-10.l42scl.hortonworks.com, port: 13562, pathComponent: attempt_1429683757595_0141_1_00_000404_0_10009_1, runDuration: 0]
2015-04-23 03:28:08,272 INFO [TezTaskEventRouter[attempt_1429683757595_0141_1_01_000143_0]] orderedgrouped.ShuffleInputEventHandlerOrderedGrouped: DME srcIdx: 143, targetIdx: 404, attemptNum: 0, payload: [hasEmptyPartitions: true, host: cn047-10.l42scl.hortonworks.com, port: 13562, pathComponent: attempt_1429683757595_0141_1_00_000404_0_10009_2, runDuration: 0]

This will fail depending on how many times _404_0 is at the top of the FileChunks list in this run.