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https://issues.apache.org/jira/browse/YARN-9947?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16966448#comment-16966448
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Hu Ziqian commented on YARN-9947:
---------------------------------
[~taoyang], [~leftnoteasy] could you help me to review this issue?
> lazy init appLogAggregatorImpl when log aggregation
> ---------------------------------------------------
>
> Key: YARN-9947
> URL: https://issues.apache.org/jira/browse/YARN-9947
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: nodemanager
> Affects Versions: 3.1.3
> Reporter: Hu Ziqian
> Assignee: Hu Ziqian
> Priority: Major
> Attachments: YARN-9947.001.patch
>
>
> This issue introduce an method to lazy init appLogAggregatorImpl, which let
> it access hdfs as later as possible (when the app finish usually), to avoid
> access hdfs at same time when restart NMs in a cluster and reduce hdfs
> pressure. Lets go into the details below.
> In current version, app log aggregator will check HDFS and try to create log
> app when init an app. This cause a problem when restart NMs in a large
> cluster with a heavy hdfs. Restart NM will init all apps on a NM and the NM
> will try to connect HDFS. If the HDFS is heavily loaded, many NMs restart at
> same time will let the hdfs not respond. The NM will wait for HDFS's response
> and RM can't get NM's heartbeat and treat all containers as timeout.
> In our product environment with 3500+ NMs, we find the NMs restart will put
> heavy pressure on HDFS and the init app's operation is blocked on accessing
> hdfs (stack attached blow), which causes all the container failed (we can
> find the container number in one NM fall to zero).
> !https://teambition-file.alibaba-inc.com/storage/011mcaf1aebf84f02a5d2c2c5fa85af80f5b?download=upload_tfs_by_description.png&Signature=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJBcHBJRCI6IjVjZDkwOTdmYjNhNDMyMjk3OTBhN2EyZiIsIl9hcHBJZCI6IjVjZDkwOTdmYjNhNDMyMjk3OTBhN2EyZiIsIl9vcmdhbml6YXRpb25JZCI6IjVjNDA1N2YwYmU4MjViMzkwNjY3YWJlZSIsImV4cCI6MTU3MjgzNzQxMywiaWF0IjoxNTcyODM3MTEzLCJyZXNvdXJjZSI6Ii9zdG9yYWdlLzAxMW1jYWYxYWViZjg0ZjAyYTVkMmMyYzVmYTg1YWY4MGY1YiJ9.JJQoQvjWdAQItQkjtdxa1SnkqJWuij_w2xq2Unoaktg!
> !https://teambition-file.alibaba-inc.com/storage/011m873079212ee7fe507ddbe163a0c07fb1?download=upload_tfs_by_description.png&Signature=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJBcHBJRCI6IjVjZDkwOTdmYjNhNDMyMjk3OTBhN2EyZiIsIl9hcHBJZCI6IjVjZDkwOTdmYjNhNDMyMjk3OTBhN2EyZiIsIl9vcmdhbml6YXRpb25JZCI6IjVjNDA1N2YwYmU4MjViMzkwNjY3YWJlZSIsImV4cCI6MTU3MjgzNzQxMywiaWF0IjoxNTcyODM3MTEzLCJyZXNvdXJjZSI6Ii9zdG9yYWdlLzAxMW04NzMwNzkyMTJlZTdmZTUwN2RkYmUxNjNhMGMwN2ZiMSJ9.kH73n6bdx8ETXsrWcBGgXGay2WP3z9nzuDlE8-RvQzs!
> We solve this problem by introduce lazy initialization in
> appLogAggregatorImpl. When init app, we just create appLogAggregatorImpl
> object with out verifyAndCreateRemoteLogDir(). We do the
> verifyAndCreateRemoteLogDir() when the app start aggregate logs. Because apps
> always are not finish or aggregate log at same time, the
> verifyAndCreateRemoteLogDir will execute dispersedly, which means NMs will
> not access hdfs at same time when they restart at same time.
>
> YARN-8418 solve the container logs' directory leaked problem by add a way to
> update credentials of NM. If we lazy init appLogAggregatorImpl, we don't need
> YARN-8418's logic because the lazy init logic happens after addCredentials
> logic, which means the credentials always refreshed before we use it.
>
> In summary, this issue do two things:
> # Introducing a lazy init logic to appLogAggregatorImpl to avoid centralized
> access HDFS when restart all NMs in a cluster.
> # Reverting YARN-8481 because the lazy init logic guarantee refreshing the
> credentials.
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