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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13726) Enforce that FileSystem initializes only a single instance of the requested FileSystem.
Date Mon, 17 Oct 2016 22:31:58 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15583706#comment-15583706
] 

Chris Nauroth commented on HADOOP-13726:
----------------------------------------

HADOOP-13727 describes a specific problem in S3A that prompted me to file this JIRA for the
FileSystem cache.  In that case, the redundant initialization caused a high number of calls
to the EC2 Instance Metadata Service, which ultimately throttled clients and caused failures.

> Enforce that FileSystem initializes only a single instance of the requested FileSystem.
> ---------------------------------------------------------------------------------------
>
>                 Key: HADOOP-13726
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13726
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>            Reporter: Chris Nauroth
>
> The {{FileSystem}} cache is intended to guarantee reuse of instances by multiple call
sites or multiple threads.  The current implementation does provide this guarantee, but there
is a brief race condition window during which multiple threads could perform redundant initialization.
 If the file system implementation has expensive initialization logic, then this is wasteful.
 This issue proposes to eliminate that race condition and guarantee initialization of only
a single instance.



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