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From "Sangjin Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9854) Configuration.set() may be called before all the deprecated keys are registered, causing inconsistent state
Date Mon, 23 Sep 2013 20:11:03 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13775613#comment-13775613
] 

Sangjin Lee commented on HADOOP-9854:
-------------------------------------

[~acmurthy], the sequence of events is a little involved. The specific combination is scalding
and cascading. The problem starts when the user sets an old key. Let's say the user set the
old key to 100 (where the default is 1).

Scalding runs the task with the ToolRunner but uses Configuration. In its tool, scalding converts
the configuration items from the Configuration into a Map<String,String> and passes
it to cascading. In cascading, using a Map as opposed to a Configuration or JobConf is a standard
mode of operation. When scalding creates the Map, it uses Configuration.iterator() to get
the values out of the Configuration. So up until this point, the deprecated keys from JobConf
have not been registered (because JobConf was not initialized), and thus the Map now contains
inconsistent values for any map-reduce-related config params. At this point, the Map has 100
under the old key, and 1 under the new key.

Once cascading receives this Map, it eventually constructs a JobConf instance using the Map.
This triggers all the deprecated keys for JobConf to be registered. And when values from Map
are set onto JobConf via set(), the new value from the Map wins (which is still the default
value, not the user-overridden value), thus wiping out the user override. The JobConf instance
now has 1 for both the new and the old keys.
                
> Configuration.set() may be called before all the deprecated keys are registered, causing
inconsistent state
> -----------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-9854
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9854
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: conf
>    Affects Versions: 2.0.5-alpha
>            Reporter: Sangjin Lee
>            Priority: Blocker
>
> Currently deprecated keys are registered at various times. Some are registered  when
the Configuration class itself is initialized, but the vast majority are registered when the
JobConf class is initialized.
> Therefore, it is entirely possible (and does happen) that Configuration.set() is called
for a key before its deprecation mapping is registered, thus leaving the internal state of
Configuration in an inconsistent state.
> We actually had this problem occur in real life, causing the set value not to be recognized.

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