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https://issues.apache.org/jira/browse/HDFS-16872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17651122#comment-17651122
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ASF GitHub Bot commented on HDFS-16872:
---------------------------------------
ChengbingLiu commented on PR #5246:
URL: https://github.com/apache/hadoop/pull/5246#issuecomment-1362517793
> So one issue I realized with this approach is that `LogThrottlingHelper`
isn't thread-safe.
We probably need to make `LogThrottlingHelper` properly threadsafe (atomics,
concurrent hash map, etc.).
IMO, to make `LogThrottlingHelper` thread-safe, it isn't enough just to make
its member variables thread-safe. For example, if we just change `Map<String,
LoggingAction> currentLogs;` to a ConcurrentHashMap, it won't help because
there are multiple gets and puts inside the `record` method.
It seems that the only way to make it thread-safe is to add `synchronized`
to `record(...)` as well as other methods. However, doing so may affect the
performance.
> Is it possible to have multiple instances of `FSEditLogLoader` or
`RedundantEditLogInputStream` running simultaneously? I think yes?
Tracing down usages of `LogThrottlingHelper` in `FSEditLogLoader` or
`RedundantEditLogInputStream`, the main usage seems to happen inside a
`FSNameSystem` writeLock/writeUnlock block, yet there might be other cases that
can have a concurrency issue.
> Fix log throttling by declaring LogThrottlingHelper as static members
> ---------------------------------------------------------------------
>
> Key: HDFS-16872
> URL: https://issues.apache.org/jira/browse/HDFS-16872
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 3.3.4
> Reporter: Chengbing Liu
> Priority: Major
> Labels: pull-request-available
>
> In our production cluster with Observer NameNode enabled, we have plenty of
> logs printed by {{FSEditLogLoader}} and {{RedundantEditLogInputStream}}. The
> {{LogThrottlingHelper}} doesn't seem to work.
> {noformat}
> 2022-10-25 09:26:50,380 INFO org.apache.hadoop.hdfs.server.namenode.FSImage:
> Start loading edits file ByteStringEditLog[17686250688, 17686250688],
> ByteStringEditLog[17686250688, 17686250688], ByteStringEditLog[17686250688,
> 17686250688] maxTxnsToRead = 9223372036854775807
> 2022-10-25 09:26:50,380 INFO
> org.apache.hadoop.hdfs.server.namenode.RedundantEditLogInputStream:
> Fast-forwarding stream 'ByteStringEditLog[17686250688, 17686250688],
> ByteStringEditLog[17686250688, 17686250688], ByteStringEditLog[17686250688,
> 17686250688]' to transaction ID 17686250688
> 2022-10-25 09:26:50,380 INFO
> org.apache.hadoop.hdfs.server.namenode.RedundantEditLogInputStream:
> Fast-forwarding stream 'ByteStringEditLog[17686250688, 17686250688]' to
> transaction ID 17686250688
> 2022-10-25 09:26:50,380 INFO org.apache.hadoop.hdfs.server.namenode.FSImage:
> Loaded 1 edits file(s) (the last named ByteStringEditLog[17686250688,
> 17686250688], ByteStringEditLog[17686250688, 17686250688],
> ByteStringEditLog[17686250688, 17686250688]) of total size 527.0, total edits
> 1.0, total load time 0.0 ms
> 2022-10-25 09:26:50,387 INFO org.apache.hadoop.hdfs.server.namenode.FSImage:
> Start loading edits file ByteStringEditLog[17686250689, 17686250693],
> ByteStringEditLog[17686250689, 17686250693], ByteStringEditLog[17686250689,
> 17686250693] maxTxnsToRead = 9223372036854775807
> 2022-10-25 09:26:50,387 INFO
> org.apache.hadoop.hdfs.server.namenode.RedundantEditLogInputStream:
> Fast-forwarding stream 'ByteStringEditLog[17686250689, 17686250693],
> ByteStringEditLog[17686250689, 17686250693], ByteStringEditLog[17686250689,
> 17686250693]' to transaction ID 17686250689
> 2022-10-25 09:26:50,387 INFO
> org.apache.hadoop.hdfs.server.namenode.RedundantEditLogInputStream:
> Fast-forwarding stream 'ByteStringEditLog[17686250689, 17686250693]' to
> transaction ID 17686250689
> 2022-10-25 09:26:50,387 INFO org.apache.hadoop.hdfs.server.namenode.FSImage:
> Loaded 1 edits file(s) (the last named ByteStringEditLog[17686250689,
> 17686250693], ByteStringEditLog[17686250689, 17686250693],
> ByteStringEditLog[17686250689, 17686250693]) of total size 890.0, total edits
> 5.0, total load time 1.0 ms
> {noformat}
> After some digging, I found the cause is that {{LogThrottlingHelper}}'s are
> declared as instance variables of all the enclosing classes, including
> {{FSImage}}, {{FSEditLogLoader}} and {{RedundantEditLogInputStream}}.
> Therefore the logging frequency will not be limited across different
> instances. For classes with only limited number of instances, such as
> {{FSImage}}, this is fine. For others whose instances are created frequently,
> such as {{FSEditLogLoader}} and {{RedundantEditLogInputStream}}, it will
> result in plenty of logs.
> This can be fixed by declaring {{LogThrottlingHelper}}'s as static members.
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