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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-4418) HDFS-347: increase default FileInputStreamCache size
Date Thu, 17 Jan 2013 05:54:23 GMT
Todd Lipcon created HDFS-4418:
---------------------------------

             Summary: HDFS-347: increase default FileInputStreamCache size
                 Key: HDFS-4418
                 URL: https://issues.apache.org/jira/browse/HDFS-4418
             Project: Hadoop HDFS
          Issue Type: Sub-task
            Reporter: Todd Lipcon
            Assignee: Todd Lipcon


The FileInputStreamCache currently defaults to holding only 10 input stream pairs (corresponding
to 10 blocks). In many HBase workloads, the region server will be issuing random reads against
a local file which is 2-4GB in size or even larger (hence 20+ blocks).

Given that the memory usage for caching these input streams is low, and applications like
HBase tend to already increase their ulimit -n substantially (eg up to 32,000), I think we
should raise the default cache size to 50 or more. In the rare case that someone has an application
which uses local reads with hundreds of open blocks and can't feasibly raise their ulimit
-n, they can lower the limit appropriately.

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