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From "Aaron Kimball (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-6420) String-to-String Maps should be embeddable in Configuration
Date Wed, 16 Dec 2009 02:06:18 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-6420?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Aaron Kimball updated HADOOP-6420:
----------------------------------

    Attachment: HADOOP-6420.8.patch

I realized after working more on MAPREDUCE-1126 that I need the ability to determine if a
map is empty or not; when I was using the HashMap-based (deep-copy) getMap(), this was accomplished
via {{Map.size() == 0}}; but determining the map's size in general requires iteration, which
we decided not to support due to the expense.

Instead I've added a sentinel value that indicates whether the map exists or not. This is
set by {{setMap()}} and can be read with {{mapExists()}}. Since we also support users creating
maps using the underlying properties (e.g., {{conf.set("foo.bar", "a"); conf.set("foo.baz",
"b"); conf.getMap("foo")}}), I've added a {{declareMap()}} method that adds the sentinel as
well. (so you could write:   {{conf.set("foo.bar", "a"); conf.set("foo.baz", "b"); conf.declareMap("foo");
assertTrue(conf.mapExists("foo")}}).  This works by creating a key named {{"foo"}} in the
Configuration whose value is {{"$MAP$"}}. 

This is necessary in MAPREDUCE-1126 to determine whether the user has properly called a metadata-API
{{setMapOutputKeyClass() / setMapOutputKeySchema()}} method, or whether we should fall back
to the deprecated {{JobConf.getMapOutputKeyClass() / JobConf.getOutputKeyClass()}} API.

> String-to-String Maps should be embeddable in Configuration
> -----------------------------------------------------------
>
>                 Key: HADOOP-6420
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6420
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: conf
>            Reporter: Aaron Kimball
>            Assignee: Aaron Kimball
>         Attachments: HADOOP-6420.2.patch, HADOOP-6420.3.patch, HADOOP-6420.4.patch, HADOOP-6420.5.patch,
HADOOP-6420.6.patch, HADOOP-6420.7.patch, HADOOP-6420.8.patch, HADOOP-6420.patch
>
>
> Per MAPREDUCE-1126, we need to be able to take a map of (key, value) pairs and embed
that inside a Configuration object.

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