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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 Sat, 17 Oct 2009 06:41:31 GMT

    [ https://issues.apache.org/jira/browse/PIG-993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12766841#action_12766841
] 

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


I think the test needs to be fixed.  It deletes 6 column groups from 6 different threads.
The spec explicitly states read accesses and parallel deletions expected to fail. But the
table is always left in consistent state. The rationale for this is that in practice these
tables are accessed from different machines and it would add unnecessary complication to support
coordinate all the readers and the writers (especially with no locking support on HDFS). Zebra
tables have no state outside the directory. This applies to writing as well.

One options I see is to make each thread make multiple attempts in case of errors. 
  

> [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: 0.6.0
>
>         Attachments: DropColumnGroupExample.java, TEST-org.apache.hadoop.zebra.io.TestCheckin.txt,
zebra-drop-cg.patch, zebra-drop-cg.patch, zebra-drop-cg.patch
>
>
> 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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