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Posted to yarn-issues@hadoop.apache.org by "He Tianyi (JIRA)" <ji...@apache.org> on 2015/09/15 12:22:45 UTC
[jira] [Commented] (YARN-4159) False-positive of ACK slow log in
DFSClient
[ https://issues.apache.org/jira/browse/YARN-4159?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14745201#comment-14745201 ]
He Tianyi commented on YARN-4159:
---------------------------------
Sorry, wrong project. Please close.
> False-positive of ACK slow log in DFSClient
> -------------------------------------------
>
> Key: YARN-4159
> URL: https://issues.apache.org/jira/browse/YARN-4159
> Project: Hadoop YARN
> Issue Type: Bug
> Components: client
> Affects Versions: 2.6.0
> Reporter: 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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