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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-993) [zebra] Abitlity to drop a column group in a table
Date Fri, 02 Oct 2009 22:50:23 GMT

    [ https://issues.apache.org/jira/browse/PIG-993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12761766#action_12761766
] 

Raghu Angadi commented on PIG-993:
----------------------------------


API  is pretty simple : {code}
class org.apache.hadoop.zebra.BasicTable {
 /** see the patch for JavaDoc and attached example for usage */

public static void dropColumnGroup(Path path,
                                   Configuration conf,   String cgName)
                               throws IOException { ... }
}
{code}

  * Table schema is not modified.  
  * this API takes a name for a column group. PIG-986 adds explicit names for CGs.
  * Once a CGs is deleted, NULL is returned for the fields that were stored in the CG. 
     ** This is the main difference between just manually deleting  a directory on filesystem
and 'properly' deleting a CG.
     ** Many changes made in other parts of zebra are related to handling the missing CGs.


> [zebra] Abitlity to drop a column group in a table
> --------------------------------------------------
>
>                 Key: PIG-993
>                 URL: https://issues.apache.org/jira/browse/PIG-993
>             Project: Pig
>          Issue Type: Bug
>            Reporter: Raghu Angadi
>            Assignee: Raghu Angadi
>             Fix For: 0.5.0
>
>
> A Zebra table is stored as multiple sub tables each containing a set of columns called
column group (CG). The user specifies how these columns are grouped while creating a table
through the _storage hint_.
> For some of the large tables, it might be necessary for users to remove a set of columns
and retain the rest. This jira provides a way for users to delete an entire column group.

> The following comments will have more details on API and the semantics. 

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