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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12219) Use optionally a TTL based cache for FSTableDescriptors#getAll() and FSTableDescriptors#TableDescriptorAndModtime()
Date Fri, 10 Oct 2014 18:36:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12219?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14167274#comment-14167274
] 

Andrew Purtell commented on HBASE-12219:
----------------------------------------

bq. I'm not really concerned about the staleness if the TTL is as short as 1 second 

Then definitely the suggested alternative could make a big difference in the number of NN
ops totally, if descriptors for a table rarely or never change.

> Use optionally a TTL based cache for FSTableDescriptors#getAll() and FSTableDescriptors#TableDescriptorAndModtime()
> -------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-12219
>                 URL: https://issues.apache.org/jira/browse/HBASE-12219
>             Project: HBase
>          Issue Type: Bug
>          Components: master
>    Affects Versions: 0.94.24, 0.99.1, 0.98.6.1
>            Reporter: Esteban Gutierrez
>            Assignee: Esteban Gutierrez
>              Labels: scalability
>
> Currently table descriptors and tables are cached once they are accessed for the first
time. Next calls to the master only require a trip to HDFS to lookup the modified time in
order to reload the table descriptors if modified. However in clusters with a large number
of tables or concurrent clients and this can be too aggressive to HDFS and the master causing
contention to process other requests. A simple solution is to have a TTL based cached for
FSTableDescriptors#getAll() and  FSTableDescriptors#TableDescriptorAndModtime() that can allow
the master to process those calls faster without causing contention without having to perform
a trip to HDFS for every call. to listtables() or getTableDescriptor()



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