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https://issues.apache.org/jira/browse/HDFS-9081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15647839#comment-15647839
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static-max commented on HDFS-9081:
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I also get this warning in my client logs, but not on any namenode or datanode.
So I think this is a rather annoying bug. I get this error with a client
application (Apache Flink) with very low throughput (1MB / minute) and all my
other Hadoop applications work without any problem.
Any work planned to fix this?
> False-positive ACK slow log in DFSClient
> ----------------------------------------
>
> Key: HDFS-9081
> URL: https://issues.apache.org/jira/browse/HDFS-9081
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.6.0
> Reporter: He Tianyi
> Assignee: He Tianyi
> Priority: Minor
>
> This issue is related with code below:
> {noformat}
> if (duration > dfsclientSlowLogThresholdMs
> && ack.getSeqno() != Packet.HEART_BEAT_SEQNO) {
> DFSClient.LOG
> .warn("Slow ReadProcessor read fields took " + duration
> + "ms (threshold=" + dfsclientSlowLogThresholdMs + "ms); ack: "
> + ack + ", targets: " + Arrays.asList(targets));
> } else if (DFSClient.LOG.isDebugEnabled()) {
> DFSClient.LOG.debug("DFSClient " + ack);
> }
> {noformat}
> DFSClient prints slow log when awaited after unexpected amount of time
> (usually 30000 ms). This is a good indicator for network or I/O performance
> issue.
> However, there is scenario that this slow log is false-positive, i.e. a
> reducer, (StageA) iterates over records with identical key, this takes
> arbitrary amount of time, but generates no output. (StageB) Then, it output
> arbitrary number of records when meet a different key.
> If one StageA lasts more than 30000 ms (as the example above), there will be
> one or more slow log generated, which is not related to any HDFS performance
> issue.
> In general cases, user should not expect this, as they could be misguided.
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