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https://issues.apache.org/jira/browse/BOOKKEEPER-215?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13258855#comment-13258855
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Flavio Junqueira commented on BOOKKEEPER-215:
---------------------------------------------
One idea occurred to me and I wanted to run it by you guys. I don't think it is
critical that we throttle for recovery, so I was wondering if it makes sense
that the calls to read entries from LedgerRecoveryOp do not try to acquire
permits. This was we avoid the problem altogether.
> Deadlock occurs under high load
> -------------------------------
>
> Key: BOOKKEEPER-215
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-215
> Project: Bookkeeper
> Issue Type: Bug
> Components: hedwig-server
> Affects Versions: 4.1.0
> Reporter: Aniruddha
> Assignee: Sijie Guo
> Priority: Critical
> Fix For: 4.1.0
>
> Attachments: BK-215.patch, BK-215.patch_v2, hedwig_ts.log
>
>
> LedgerHandle uses a Semaphore(opCounterSem) with a default value of 5000
> permits to implement throttling for outstanding requests. This is causing a
> deadlock under high load. What I've observed is the following - There are a
> fixed number of threads created by OrderedSafeExecutor(mainWorkerPool in
> BookKeeper) and this is used to execute operations by PerChannelBookieClient.
> Under high load, the bookies are not able to satisfy requests at the rate at
> which they are being generated. This exhausts all permits in the Semaphore
> and any further operations block on lh.opCounterSem.acquire(). In this
> scenario, if the connection to the bookies is shut down, channelDisconnected
> in PerChannelBookieClient tries to error out all outstanding entries. The
> errorOutReadKey and errorOutAddKey functions enqueue these operations in the
> same mainWorkerPool, all threads in which are blocked on acquire. So,
> handleBookieFailure is never executed and the server stops responding.
> Blocking operations in a fixed size thread pool doesn't sound quite right.
> Temporarily, I fixed this by having another ExecutorService for every
> PerChannelBookieClient and queuing the operations from the errorOut*
> functions in it, but this is just a quick fix. I feel that the server
> shouldn't rely on LedgerHandle to throttle connections, but do this itself.
> Any other ideas on how to fix this? I'd be happy to contribute a patch.
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