Rajesh Balamohan created TEZ-4211:
-------------------------------------
Summary: Optimise MergeManager final merge
Key: TEZ-4211
URL: https://issues.apache.org/jira/browse/TEZ-4211
Project: Apache Tez
Issue Type: Bug
Reporter: Rajesh Balamohan
There are cases, when entire data is held in memory and no disk segments are
present in MergeManager. Currently, mergemanager spills mem segments to disk
before proceeding.
[https://github.com/apache/tez/blob/master/tez-runtime-library/src/main/java/org/apache/tez/runtime/library/common/shuffle/orderedgrouped/MergeManager.java#L1184]
{code:java}
if (numMemDiskSegments > 0 && ioSortFactor > onDiskMapOutputs.size()) {
...
..
TezMerger.writeFile(rIter, writer, progressable,
TezRuntimeConfiguration.TEZ_RUNTIME_RECORDS_BEFORE_PROGRESS_DEFAULT);
...
..
{code}
This can be optimised not to spill to disk when only mem segments are present.
Snippet from logs in one of the apps (Q78)
{noformat}
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=839646500 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=859378362 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=856145179 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=849878734 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=842666749 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=839533127 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=860448335 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=844468505 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=850099810 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=849206236 and #onDiskOutputs=0,
size=0
[ShuffleAndMergeRunner {Map_1} ()]
org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager:
finalMerge with #inMemoryOutputs=4112, size=840238680 and #onDiskOutputs=0,
size=0
{noformat}
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