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Chris Douglas commented on MAPREDUCE-5821: ------------------------------------------ Sure, I can take a look later this week if it can wait. > IFile merge allocates new byte array for every value > ---------------------------------------------------- > > Key: MAPREDUCE-5821 > URL: https://issues.apache.org/jira/browse/MAPREDUCE-5821 > Project: Hadoop Map/Reduce > Issue Type: Bug > Components: performance, task > Affects Versions: 2.4.1 > Reporter: Todd Lipcon > Assignee: Todd Lipcon > Attachments: after-patch.png, before-patch.png, mapreduce-5821.txt, > mapreduce-5821.txt > > > I wrote a standalone benchmark of the MapOutputBuffer and found that it did a > lot of allocations during the merge phase. After looking at an allocation > profile, I found that IFile.Reader.nextRawValue() would always allocate a new > byte array for every value, so the allocation rate goes way up during the > merge phase of the mapper. I imagine this also affects the reducer input, > though I didn't profile that. -- This message was sent by Atlassian JIRA (v6.2#6252)