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From "static-max (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9081) False-positive ACK slow log in DFSClient
Date Tue, 08 Nov 2016 15:22:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15647839#comment-15647839
] 

static-max commented on HDFS-9081:
----------------------------------

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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