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From "Bryan Duxbury (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4346) Hadoop triggers a "soft" fd leak.
Date Tue, 07 Oct 2008 01:09:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4346?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637340#action_12637340
] 

Bryan Duxbury commented on HADOOP-4346:
---------------------------------------

Originally I had 1024 per machine. I recently increased it to 4096 and I haven't seen the
problem as much, but it was intermittent before, so I don't know if it's resolved or not.

> Hadoop triggers a "soft" fd leak. 
> ----------------------------------
>
>                 Key: HADOOP-4346
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4346
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: io
>    Affects Versions: 0.17.0
>            Reporter: Raghu Angadi
>            Assignee: Raghu Angadi
>         Attachments: HADOOP-4346-branch-18.patch, HADOOP-4346.patch
>
>
> Starting with Hadoop-0.17, most of the network I/O uses non-blocking NIO channels. Normal
blocking reads and writes are handled by Hadoop and use our own cache of selectors. This cache
suites well for Hadoop where I/O often occurs on many short lived threads. Number of fds consumed
is proportional to number of threads currently blocked. 
> If blocking I/O is done using java.*, Sun's implementation uses internal per-thread selectors.
These selectors are closed using {{sun.misc.Cleaner}}. Looks like this cleaning is kind of
like finalizers and tied to GC. This is pretty ill suited if we have many threads that are
short lived. Until GC happens, number of these selectors keeps growing. Each selector consumes
3 fds.
> Though blocking read and write are handled by Hadoop, {{connect()}} is still the default
implementation that uses per-thread selector. 
> Koji helped a lot in tracking this. Some sections from 'jmap' output and other info 
Koji collected led to this suspicion and will include that in the next comment.
> One solution might be to handle connect() also in Hadoop using our selectors.

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