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https://issues.apache.org/jira/browse/TEZ-3709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15995850#comment-15995850
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Jonathan Eagles commented on TEZ-3709:
--------------------------------------
Example performance gains
| task attempt | duration w/o patch | duration w/ patch | NUM_SHUFFLE_INPUTS |
SHUFFLE_BYTES |
| 0 | 22m 30s 458ms | 7m 34s 752ms | 1238533 | 138894095 |
> 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
>
>
> 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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