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https://issues.apache.org/jira/browse/YARN-4720?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15163918#comment-15163918
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Ming Ma commented on YARN-4720:
-------------------------------
Thanks [~hex108] for the update. The patch looks good overall. It does change
the following behaviors.
* When {{pendingContainerInThisCycle}} is empty, NM will skip sending the
{{LogAggregationReport}} with {{LogAggregationStatus.RUNNING}}. It means for a
long running service, it is possible for a yarn client to get
{{LogAggregationStatus.NOT_START}} when it calls
{{ApplicationClientProtocol#getApplicationReport}} if the long running service
doesn't generate any log. Without the patch, NM will send
{{LogAggregationStatus.RUNNING}} regardless. So it might be better to still
send {{LogAggregationStatus.RUNNING}} regardless.
* When {{LogWriter}} creation throws exception and {{appFinished}} is true, NM
will send a {{LogAggregationReport}} with {{LogAggregationStatus.SUCCEEDED}}.
Without the patch, NM won't send any final {{LogAggregationReport}}. Maybe it
is better to update the patch to send {{LogAggregationStatus.FAILED}} for such
scenario.
> Skip unnecessary NN operations in log aggregation
> -------------------------------------------------
>
> Key: YARN-4720
> URL: https://issues.apache.org/jira/browse/YARN-4720
> Project: Hadoop YARN
> Issue Type: Improvement
> Reporter: Ming Ma
> Assignee: Jun Gong
> Attachments: YARN-4720.01.patch, YARN-4720.02.patch
>
>
> Log aggregation service could have unnecessary NN operations in the following
> scenarios:
> * No new local log has been created since the last upload for the long
> running service scenario.
> * NM uses {{ContainerLogAggregationPolicy}} that skips log aggregation for
> certain containers.
> In the following code snippet, even though {{pendingContainerInThisCycle}} is
> empty, it still creates the writer and then removes the file later. Thus it
> introduces unnecessary create/getfileinfo/delete NN calls when NM doesn't
> aggregate logs for an app.
>
> {noformat}
> AppLogAggregatorImpl.java
> ......
> writer =
> new LogWriter(this.conf, this.remoteNodeTmpLogFileForApp,
> this.userUgi);
> ......
> for (ContainerId container : pendingContainerInThisCycle) {
> ......
> }
> ......
> if (remoteFS.exists(remoteNodeTmpLogFileForApp)) {
> if (rename) {
> remoteFS.rename(remoteNodeTmpLogFileForApp, renamedPath);
> } else {
> remoteFS.delete(remoteNodeTmpLogFileForApp, false);
> }
> }
> ......
> {noformat}
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