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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1283) Eliminate internal UTF8 to String and vice versa conversions in the name-node.
Date Mon, 18 Jun 2007 17:26:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1283?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12505894
] 

Doug Cutting commented on HADOOP-1283:
--------------------------------------

> AFAIK UTF8 and BytesWritable serializations differ only in the type of the length field.

I think UTF8 may also use "modified UTF-8" when encoding Strings.

http://java.sun.com/javase/6/docs/api/java/io/DataInput.html#modified-utf-8

Note that, for back-compatibility, we can still read files written with UTF8 once UTF8 is
gone by using DataInput, since the format is identical.  UTF8's implementation was optimized,
but should be equivalent.

> Eliminate internal UTF8 to String and vice versa conversions in the name-node.
> ------------------------------------------------------------------------------
>
>                 Key: HADOOP-1283
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1283
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.12.0
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>         Attachments: EliminateUTF8.patch
>
>
> We have internal conversions of those two types inside name-node code. One example:
> NameNode.complete(String src, String clientName)
> then it calls
> FSNamesystem.completeFile(new UTF8(src), new UTF8(clientName));
> which in turn finally calls
> FSDirectory.addNode(path.toString(), newNode )
> and in another place
> FSDirectory.getNode(src.toString())
> So we have several conversions of the same parameter back and forth during computation.
> We should keep the parameter type consistent within different methods.
> The question is, which type should be used: String or Text.
> From previous discussions I remember that Text is more efficient in space and time for
non ASCII
> data. Here we mostly deal with file names and network addresses, which are ASCII.
> Does it make sense to use Text in this case?
> UTF8 is also used as a key in two maps: pendingCreates and leases.
> This should be replaced too.

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