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https://issues.apache.org/jira/browse/HADOOP-11238?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chris Li reassigned HADOOP-11238:
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Assignee: Chris Li
> Group cache expiry causes namenode slowdown
> -------------------------------------------
>
> Key: HADOOP-11238
> URL: https://issues.apache.org/jira/browse/HADOOP-11238
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 2.5.1
> Reporter: Chris Li
> Assignee: Chris Li
> Priority: Minor
>
> Our namenode pauses for 12-60 seconds several times every hour or so. During
> these pauses, no new requests can come in.
> Around the time of pauses, we have log messages such as:
> 2014-10-22 13:24:22,688 WARN org.apache.hadoop.security.Groups: Potential
> performance problem: getGroups(user=xxxxx) took 34507 milliseconds.
> The current theory is:
> 1. Groups has a cache that is refreshed periodically.
> 2. When the cache is cleared, we have a thundering herd effect which
> overwhelms our LDAP servers (we are using ShellBasedUnixGroupsMapping with
> sssd, how this happens has yet to be established)
> 3. group resolution queries begin to take longer, I've observed it taking 1.2
> seconds instead of the usual 0.01-0.03 seconds when measuring in the shell
> `time groups myself`
> 4. If there is mutual exclusion somewhere along this path, a 1 second pause
> could lead to a 60 second pause as all the threads compete for the resource.
> The exact cause hasn't been established
> Potential solutions include:
> 1. Increasing group cache time, which will make the issue less frequent
> 2. Rolling evictions of the cache so we prevent the large spike in LDAP
> queries
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