[
https://issues.apache.org/jira/browse/HDFS-9081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14942008#comment-14942008
]
He Tianyi commented on HDFS-9081:
---------------------------------
I think code below in {{waitForAckedSeqno}} is already a good indicator of slow
acks:
{noformat}
long duration = Time.monotonicNow() - begin;
if (duration > dfsclientSlowLogThresholdMs) {
LOG.warn("Slow waitForAckedSeqno took " + duration
+ "ms (threshold=" + dfsclientSlowLogThresholdMs + "ms)");
}
{noformat}
While slow log in {{ResponseProcessor}} indicates either slow data producer or
slow ack. I'd suggest more informative slow log.
> 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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
