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https://issues.apache.org/jira/browse/TEZ-3709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15997577#comment-15997577
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Jonathan Eagles commented on TEZ-3709:
--------------------------------------
[~rajesh.balamohan], found one more example of remove(0) in
createInMemorySegments that saved another 6-7 minutes for this task attempt.
> TezMerger is slow for high number of segments
> ---------------------------------------------
>
> Key: TEZ-3709
> URL: https://issues.apache.org/jira/browse/TEZ-3709
> Project: Apache Tez
> Issue Type: Bug
> Reporter: Jonathan Eagles
> Assignee: Jonathan Eagles
> Labels: performance
> Attachments: TEZ-3709.1.patch, TEZ-3709.2.patch, TEZ-3709.3.patch
>
>
> The below code is a bad performer at scale since it has to memcpy the whole
> list of segments for each item in the batch instead of of just once per batch.
> This is true for both computeBytesInMerges and getSegmentDescriptors.
> {code}
> for (int i = 0; i < batch; i++) {
> ArrayList#remove(0)
> }
> {code}
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