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https://issues.apache.org/jira/browse/PIG-734?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12707174#action_12707174
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Alan Gates commented on PIG-734:
--------------------------------

For serialization, a type discovery has to happen on every key, because there's 
no guarantee that every key is of the same type.  By forcing all keys to 
strings we're eliminating this step, thus speeding the serialization 
significantly.

> Non-string keys in maps
> -----------------------
>
>                 Key: PIG-734
>                 URL: https://issues.apache.org/jira/browse/PIG-734
>             Project: Pig
>          Issue Type: Bug
>    Affects Versions: 0.2.0
>            Reporter: Alan Gates
>            Assignee: Alan Gates
>            Priority: Minor
>             Fix For: 0.3.0
>
>         Attachments: PIG-734.patch
>
>
> With the addition of types to pig, maps were changed to allow any atomic type 
> to be a key.  However, in practice we do not see people using keys other than 
> strings.  And allowing multiple types is causing us issues in serializing 
> data (we have to check what every key type is) and in the design for non-java 
> UDFs (since many scripting languages include associative arrays such as 
> Perl's hash).
> So I propose we scope back maps to only have string keys.  This would be a 
> non-compatible change.  But I am not aware of anyone using non-string keys, 
> so hopefully it would have little or no impact.

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