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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5781) Use a map to record the mapping between FSEditLogOpCode and the corresponding byte value
Date Mon, 20 Jan 2014 19:51:32 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5781?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13876795#comment-13876795
] 

Colin Patrick McCabe commented on HDFS-5781:
--------------------------------------------

I agree that using {{Enum#values}} directly is not the right thing here.  It might make backports
difficult, as you commented.

How about just using an array that might contain some nulls?  A hash map looks like overkill
because there aren't that many entries, and they key numbers are all close together.

> Use a map to record the mapping between FSEditLogOpCode and the corresponding byte value
> ----------------------------------------------------------------------------------------
>
>                 Key: HDFS-5781
>                 URL: https://issues.apache.org/jira/browse/HDFS-5781
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.4.0
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>         Attachments: HDFS-5781.000.patch
>
>
> HDFS-5674 uses Enum.values and enum.ordinal to identify an editlog op for a given byte
value. While improving the efficiency, it may cause issue. E.g., when several new editlog
ops are added to trunk around the same time (for several different new features), it is hard
to backport the editlog ops with larger byte values to branch-2 before those with smaller
values, since there will be gaps in the byte values of the enum. 
> This jira plans to still use a map to record the mapping between editlog ops and their
byte values. 



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