[
https://issues.apache.org/jira/browse/HADOOP-4952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12663231#action_12663231
]
Sanjay Radia commented on HADOOP-4952:
--------------------------------------
Thanks for the clarifications; I understand the issue better.
>> In my proposal the libray writer will have to add a line
>> "Files.importConfig(configArg)".
>That does not work for multi-threaded applications, where different threads
>are configured differently.
Depends on how you implement it. Thread local variables (as we do for the UGI
credentials) would address MT..
We have at least the following 3 options
1) Class with static methods (as per patch) using thread local variables to
store the
default config.
2) Class with static methods and a config parameter for each method
3)Class with instance methods
{code}
Class Files {
static Files defaultConf();
Files(config)
//open, create etc are all instance methods
}
myFiles = Files.defaultConf(); // common usage
myFiles = new Files(myConf); // for those that want a specific conf
myFiles.create(...)
{code}
> Improved files system interface for the application writer.
> -----------------------------------------------------------
>
> Key: HADOOP-4952
> URL: https://issues.apache.org/jira/browse/HADOOP-4952
> Project: Hadoop Core
> Issue Type: Improvement
> Affects Versions: 0.21.0
> Reporter: Sanjay Radia
> Assignee: Sanjay Radia
> Attachments: Files.java
>
>
> Currently the FIleSystem interface serves two purposes:
> - an application writer's interface for using the Hadoop file system
> - a file system implementer's interface (e.g. hdfs, local file system, kfs,
> etc)
> This Jira proposes that we provide a simpler interfaces for the application
> writer and leave the FilsSystem interface for the implementer of a
> filesystem.
> - Filesystem interface has a confusing set of methods for the application
> writer
> - We could make it easier to take advantage of the URI file naming
> ** Current approach is to get FileSystem instance by supplying the URI and
> then access that name space. It is consistent for the FileSystem instance to
> not accept URIs for other schemes, but we can do better.
> ** The special copyFromLocalFIle can be generalized as a copyFile where the
> src or target can be generalized to any URI, including the local one.
> ** The proposed scheme (below) simplifies this.
> - The client side config can be simplified.
> ** New config() by default uses the default config. Since this is the common
> usage pattern, one should not need to always pass the config as a parameter
> when accessing the file system.
> -
> ** It does not handle multiple file systems too well. Today a site.xml is
> derived from a single Hadoop cluster. This does not make sense for multiple
> Hadoop clusters which may have different defaults.
> ** Further one should need very little to configure the client side:
> *** Default files system.
> *** Block size
> *** Replication factor
> *** Scheme to class mapping
> ** It should be possible to take Blocksize and replication factors defaults
> from the target file system, rather then the client size config. I am not
> suggesting we don't allow setting client side defaults, but most clients do
> not care and would find it simpler to take the defaults for their systems
> from the target file system.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
