[jira] [Created] (HDFS-14297) Add cache for getContentSummary() result

["Tao Jie (JIRA)" <ji...@apache.org>]

Tao Jie created HDFS-14297:
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             Summary: Add cache for getContentSummary() result
                 Key: HDFS-14297
                 URL: https://issues.apache.org/jira/browse/HDFS-14297
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Tao Jie


In a large HDFS cluster, calling {{getContentSummary}} for a directory with large amount of files is very expensive. In a certain cluster with more than 100 million files, calling {{getContentSummary}} may take more than 10s and it will hold fsnamesystem lock for such a long time.
In our cluster, there are several peripheral systems calling {{getContentSummary}} periodically to monitor the status of dirs. Actually we don't need the very accurate result in most cases. We could keep a cache for those contentSummary result in namenode, with which we could avoid repeated heavy request in a span. Also we should add more restrictions to  this cache: 1,its size should be limited and it should be LRU, 2, only result of heavy request would be  added to this cache, eg, rpctime over 1000ms.
Any thought?



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