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https://issues.apache.org/jira/browse/HIVE-24569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17266250#comment-17266250
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Jesus Camacho Rodriguez commented on HIVE-24569:
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[~prasanthj], [~mustafaiman], could any of you review this patch? Thanks
> LLAP daemon leaks file descriptors/log4j appenders
> --------------------------------------------------
>
> Key: HIVE-24569
> URL: https://issues.apache.org/jira/browse/HIVE-24569
> Project: Hive
> Issue Type: Bug
> Components: llap
> Affects Versions: 2.2.0
> Reporter: Stamatis Zampetakis
> Assignee: Stamatis Zampetakis
> Priority: Major
> Labels: pull-request-available
> Fix For: 4.0.0
>
> Attachments: llap-appender-gc-roots.png
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> With HIVE-9756 query logs in LLAP are directed to different files (file per
> query) using a Log4j2 routing appender. Without a purge policy in place,
> appenders are created dynamically by the routing appender, one for each
> query, and remain in memory forever. The dynamic appenders write to files so
> each appender holds to a file descriptor.
> Further work HIVE-14224 has mitigated the issue by introducing a custom
> purging policy (LlapRoutingAppenderPurgePolicy) which deletes the dynamic
> appenders (and closes the respective files) when the query is completed
> (org.apache.hadoop.hive.llap.daemon.impl.QueryTracker#handleLogOnQueryCompletion).
>
> However, in the presence of multiple threads appending to the logs there are
> race conditions. In an internal Hive cluster the number of file descriptors
> started going up approx one descriptor leaking per query. After some
> debugging it turns out that one thread (running the
> QueryTracker#handleLogOnQueryCompletion) signals that the query has finished
> and thus the purge policy should get rid of the respective appender (and
> close the file) while another (Task-Executor-0) attempts to append another
> log message for the same query. The initial appender is closed after the
> request from the query tracker but a new one is created to accomodate the
> message from the task executor and the latter is never removed thus creating
> a leak.
> Similar leaks have been identified and fixed for HS2 with the most similar
> one being that described
> [here|https://issues.apache.org/jira/browse/HIVE-22753?focusedCommentId=17021041&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17021041].
>
> The problem relies on the timing of threads so it may not manifestate in all
> versions between 2.2.0 and 4.0.0. Usually the leak can be seen either via
> lsof (or other similar command) with the following output:
> {noformat}
> # 1494391 is the PID of the LLAP daemon process
> ls -ltr /proc/1494391/fd
> ...
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 978 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121724_66ce273d-54a9-4dcd-a9fb-20cb5691cef7-dag_1608659125567_0008_194.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 977 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121804_ce53eeb5-c73f-4999-b7a4-b4dd04d4e4de-dag_1608659125567_0008_197.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 974 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224122002_1693bd7d-2f0e-4673-a8d1-b7cb14a02204-dag_1608659125567_0008_204.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 989 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121909_6a56218f-06c7-4906-9907-4b6dd824b100-dag_1608659125567_0008_201.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 984 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121754_78ef49a0-bc23-478f-9a16-87fa25e7a287-dag_1608659125567_0008_196.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 983 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121855_e65b9ebf-b2ec-4159-9570-1904442b7048-dag_1608659125567_0008_200.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 981 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121818_e9051ae3-1316-46af-aabb-22c53ed2fda7-dag_1608659125567_0008_198.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 980 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121744_fcf37921-4351-4368-95ee-b5be2592d89a-dag_1608659125567_0008_195.log
> lrwx------ 1 hive hadoop 64 Dec 24 12:08 979 ->
> /hadoop/yarn/log/application_1608659125567_0006/container_e04_1608659125567_0006_01_000002/hive_20201224121837_e80c0024-f6bc-4b3c-85ed-5c0c85c55787-dag_1608659125567_0008_199.log
> {noformat}
> or in the heap dump with many appenders (in my case {{LlapWrappedAppender}})
> holding indirectly open file descriptors:
> !llap-appender-gc-roots.png!
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