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From "Chris Douglas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2025) Instantiating a FileSystem object should guarantee the existence of the working directory
Date Thu, 11 Oct 2007 22:30:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12534177

Chris Douglas commented on HADOOP-2025:

Automatically creating a working directory may become awkward with permissions and when delegating
tasks to an agent. Further, creating a default place for a user's data should be part of adding
that user to the system, not executing a task.

Requesting a "home" directory for a given set of credentials- rather than a default "working
directory"- from a FileSystem seems more correct; the working directory seems like FileSystem
state owned by an application (i.e. the FileSystem object). If one wants to resolve relative
paths, the working directory must be set first on the particular instance.

This way, relative Paths can only be resolved against a FileSystem where the working directory
is set, absolute Paths are always OK, FileSystems can return a default directory for a given
user (but not in general), and all Paths from a FileSystem are fully qualified (HADOOP-1909).

At the moment, the working directory is set by the TaskTracker (to the property provided)
and by IsolationRunner (for local, temporary storage). It is used sparingly, but notably by
applications like FsShell and distcp (where reasonable defaults can be set and checked). Are
there other places where this is relied on that might make effecting this change more difficult?

> Instantiating a FileSystem object should guarantee the existence of the working directory
> -----------------------------------------------------------------------------------------
>                 Key: HADOOP-2025
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2025
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: fs
>    Affects Versions: 0.14.1
>            Reporter: Sameer Paranjpye
>             Fix For: 0.16.0
> Issues like HADOOP-1891 and HADOOP-1916 illustrate the need for this behavior.
> In HADOOP-1916 the problem is that the default working directory for a user on HDFS '/user/<username>'
does not exist. This results in the command 'hadoop dfs -copyFromLocal foo ." creating a *file*
called /user/<username> and copying the contents of the file 'foo' into this file.
> HADOOP-1891 is basically the same problem. The problem that Olga observed was that copying
a file to '.' on HDFS when her 'home directory' did not exist resulted in the creation of
a file with the path as her home directory. The problem is incorrectly filed as a bug in the
Path class. The behavior of Path is correct, as Doug points out, it is perfectly reasonable
for Path(".") to convert to an empty path. When this empty path is resolved in HDFS or any
other filesystem the resolution to '/user/<username>' is also correct (at least for
HDFS). The problem IMO is that the existence of the working directory is not guaranteed.
> When I log in to a machine my default working directory is '/home/sameerp' and filesystem
operations that I execute with relative paths all work correctly because this directory exists.
My home directory lives on a filer, in the event of it being unmountable the default working
directory I get is '/' which also is guaranteed to exist.
> In the context of Hadoop, instantiating a FileSystem object is the analogue of logging
in and should result in a working directory whose existence has been validated. In the case
of HDFS this should be '/user/<username>' or '/' if the directory does not exist.

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