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https://issues.apache.org/jira/browse/HDFS-11900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16028594#comment-16028594
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John Zhuge edited comment on HDFS-11900 at 5/30/17 1:30 AM:
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There were related discussions in the original HDFS-5776. The rationale behind
the static pool was that too many threads with many DFSClients.
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https://issues.apache.org/jira/browse/HDFS-5776?focusedCommentId=13879476&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13879476
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https://issues.apache.org/jira/browse/HDFS-5776?focusedCommentId=13880280&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13880280
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https://issues.apache.org/jira/browse/HDFS-5776?focusedCommentId=13882606&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13882606
So per-client thread pool is not desirable. And shared thread pool does manage
the resource more efficiently. However still do not like the "static" part; DI
may be better.
was (Author: jzhuge):
There were related discussions in the original HDFS-5776. The rationale behind
the static pool was that too many threads with many DFSClients if pool size is
big.
*
https://issues.apache.org/jira/browse/HDFS-5776?focusedCommentId=13879476&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13879476
*
https://issues.apache.org/jira/browse/HDFS-5776?focusedCommentId=13880280&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13880280
*
https://issues.apache.org/jira/browse/HDFS-5776?focusedCommentId=13882606&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13882606
So per-client thread pool is desirable. And shared thread pool does manage the
resource more efficiently. However still do not like the "static" part; DI may
be better.
> initThreadsNumForHedgedReads does not synchronize access to the static pool
> ---------------------------------------------------------------------------
>
> Key: HDFS-11900
> URL: https://issues.apache.org/jira/browse/HDFS-11900
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 2.8.0
> Reporter: John Zhuge
>
> *Non-static* synchronized method initThreadsNumForHedgedReads can't
> synchronize the access to the *static* class variable HEDGED_READ_THREAD_POOL.
> {code}
> private static ThreadPoolExecutor HEDGED_READ_THREAD_POOL;
> ...
> private synchronized void initThreadsNumForHedgedReads(int num) {
> {code}
> 2 DFS clients may update the same static variable in a race because the lock
> is on each DFS client object, not on the shared DFSClient class object.
> There are 2 possible fixes:
> 1. "Global thread pool": Change initThreadsNumForHedgedReads to static
> 2. "Per-client thread pool": Change HEDGED_READ_THREAD_POOL to non-static
> From the description for property {{dfs.client.hedged.read.threadpool.size}}:
> {quote}
> to a positive number. The threadpool size is how many threads to dedicate
> to the running of these 'hedged', concurrent reads in your client.
> {quote}
> it seems to indicate the thread pool is per DFS client.
> Let's assume we go with #1 "Global thread pool". One DFS client has the
> property set to 10 in its config, while the other client has the property set
> to 5 in its config, what is supposed to the size of the global thread pool?
> 5? 10? Or 15?
> The 2nd fix seems more reasonable to me.
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