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https://issues.apache.org/jira/browse/TEZ-2214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14376374#comment-14376374
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Hitesh Shah commented on TEZ-2214:
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[~rajesh.balamohan] question on the newly added invocation to
"startMemToDiskMerge". What happens when startMemToDiskMerge() is called while
a merge is in progress? It seems like startMemToDiskMerge() is a no-op when
that happens.
> FetcherOrderedGrouped can get stuck indefinitely when MergeManager misses
> memToDiskMerging
> ------------------------------------------------------------------------------------------
>
> Key: TEZ-2214
> URL: https://issues.apache.org/jira/browse/TEZ-2214
> Project: Apache Tez
> Issue Type: Bug
> Reporter: Rajesh Balamohan
> Assignee: Rajesh Balamohan
> Attachments: TEZ-2214.1.patch
>
>
> Scenario:
> - commitMemory & usedMemory are beyond their allowed threshold.
> - InMemoryMerge kicks off and is in the process of flushing memory contents
> to disk
> - As it progresses, it releases memory segments as well (but not yet over).
> - Fetchers who need memory < maxSingleShuffleLimit, get scheduled.
> - If fetchers are fast, this quickly adds up to commitMemory & usedMemory.
> Since InMemoryMerge is already in progress, this wouldn't trigger another
> merge().
> - Pretty soon all fetchers would be stalled and get into the following state.
> {noformat}
> Thread 9351: (state = BLOCKED)
> - java.lang.Object.wait(long) @bci=0 (Compiled frame; information may be
> imprecise)
> - java.lang.Object.wait() @bci=2, line=502 (Compiled frame)
> -
> org.apache.tez.runtime.library.common.shuffle.orderedgrouped.MergeManager.waitForShuffleToMergeMemory()
> @bci=17, line=337 (Interpreted frame)
> -
> org.apache.tez.runtime.library.common.shuffle.orderedgrouped.FetcherOrderedGrouped.run()
> @bci=34, line=157 (Interpreted frame)
> {noformat}
> - Even if InMemoryMerger completes, "commitedMem & usedMem" are beyond their
> threshold and no other fetcher threads (all are in stalled state) are there
> to release memory. This causes fetchers to wait indefinitely.
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