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From "Suresh Srinivas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7973) DistributedFileSystem close has severe consequences
Date Fri, 13 Jan 2012 18:24:39 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7973?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13185733#comment-13185733
] 

Suresh Srinivas commented on HADOOP-7973:
-----------------------------------------

Some comments:
bq. a decision was made on an earlier jira to not add reference counting to cached filesystem
objects
Reference counting will not work. One could get a file system instance and pass it to others
and then close it. This kind of code might exist in the framework.

bq. DistributedFileSystem#close becomes a no-op. The finalizer will close the DFSClient.
What is the finalizer - java finalizer? or you mean garbage collection?

File system cache has been a problem that has been lurking for a while. App is expected to
write the correct code - that is if the file system is closed, do not use it post that. However
I am not sure if apps do handle this correctly.

Other alternative solution is to disable cache. This is already configurable. See the following
snippet in FileSystem.java
{noformat}
    String disableCacheName = String.format("fs.%s.impl.disable.cache", scheme);
    if (conf.getBoolean(disableCacheName, false)) {
      return createFileSystem(uri, conf);
    }
{noformat}


                
> DistributedFileSystem close has severe consequences
> ---------------------------------------------------
>
>                 Key: HADOOP-7973
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7973
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: fs
>    Affects Versions: 1.0.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Blocker
>         Attachments: HADOOP-7973.patch
>
>
> The way {{FileSystem#close}} works is very problematic.  Since the {{FileSystems}} are
cached, any {{close}} by any caller will cause problems for every other reference to it. 
Will add more detail in the comments.

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