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From "Jakob Homan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5438) Merge FileSystem.create and FileSystem.append
Date Thu, 23 Jul 2009 21:23:14 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5438?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12734792#action_12734792
] 

Jakob Homan commented on HADOOP-5438:
-------------------------------------

So, as committed there are now six create methods that take a boolean value as to whether
or not overwrite (and converts them to an enumset) and one create method that takes an EnumSet.
 HADOOP-3252 will definitely help with this, but this still seems odd and counterintuitive.
 If we have the CreateFlag enum, we should use it everywhere.  Otherwise the methods are a
bit confusing - a user will sit there going 'why are there so many create methods and why
is there is this odd one out - isn't overwrite boolean the same as the createflag enum?'

If there weren't so many different create methods, I would suggest having one each for just
the Enum value and and equivalent one that takes an enumset, so that if you just wanted to
overwrite you could just use the one that takes the enum, and the convenience method would
jam it into an enumset.  It's too bad Java won't automatically convert a single enum into
an enumset when necessary.

> Merge FileSystem.create and FileSystem.append
> ---------------------------------------------
>
>                 Key: HADOOP-5438
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5438
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>            Reporter: He Yongqiang
>            Assignee: He Yongqiang
>             Fix For: 0.21.0
>
>         Attachments: Hadoop-5438(2009-04-06).patch, Hadoop-5438-2009-03-30.patch, Hadoop-5438-2009-03-31-2.patch,
Hadoop-5438-2009-03-31.patch, Hadoop-5438-2009-05-10.patch, Hadoop-5438-2009-05-15.patch,
Hadoop-5438-2009-05-19.patch, Hadoop-5438-2009-05-5.patch
>
>
> Currently, when a user wants to modify a file, the user first calls exists() to know
if this file is already there. And then uses create() or append() according to whether the
file exists or not.
> the code looks like:
> {code}
> FSDataOutputStream out_1 = null;
> if (fs.exists(path_1))
>    out_1 = fs.append(path_1);
> else
>    out_1 = fs.create(path_1);
> {code}
> . On the performace side,It involes two RPCs. On the easy-of-use side, it is not very
convient in contrast to the traditional open interface.
> It will more complicate if there is a overwrite parameter specified. I donot know whether
there is a bug about 'overwrite' in 0.19, some times it takes a long time for overwrite creates
to reture. So i make the write file code with overwrite param works like:
> {code}
> boolean exists = fs.exists(name);
> if (overwrite) {
>     if (exists)
>        fs.delete(name, true);
>      this.out = fs.create(name, overwrite, bufferSize, replication,
> 				    blockSize, progress);
>      this.currentRowID = 0;
>  } else {
>    if (!exists)
> 	this.out = fs.create(name, overwrite, bufferSize,
> 					replication, blockSize, progress);
>    else
> 	this.out = fs.append(name, bufferSize, progress);
> {code}
> Some code statements there are really redundant and not needed, especialy with the delete().
But without deleting first, the overwrite takes a long time to reture.
> BTW, i will create another issue about the overwrite problem. If it is not a bug at all
or a duplicate, someone please close it.

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