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From "Pradeep Kamath (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-953) Enable merge join in pig to work with loaders and store functions which can internally index sorted data
Date Mon, 28 Sep 2009 22:49:16 GMT

    [ https://issues.apache.org/jira/browse/PIG-953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12760423#action_12760423

Pradeep Kamath commented on PIG-953:

Here is a proposal for dealing with Sort Column information in SortInfo. Rather than giving
Arraylist of column names and separate array list of asc/desc flags, it would be good to have
a unified structure containing both pieces of information per sort column. Also there are
use cases for providing column names (zebra) and for them being optional and providing column
positions instead which some other loader /optimizer might find useful. The type of the column
might also be useful if available. Hence, the proposal is to have a SortColumn class with
the following attributes : column name, column position (zero based index), column type, asc/desc
flag. Then in SortInfo there would be a List<SortColumn> which would be available through
a getter. This should address both the concerns above. Callers will need to explicity check
for null column names and UNKNOWN column type since these two scenarios may occur if schema
is not available for pig runtime to provide the information.


> Enable merge join in pig to work with loaders and store functions which can internally
index sorted data 
> ---------------------------------------------------------------------------------------------------------
>                 Key: PIG-953
>                 URL: https://issues.apache.org/jira/browse/PIG-953
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: 0.3.0
>            Reporter: Pradeep Kamath
>            Assignee: Pradeep Kamath
>         Attachments: PIG-953-2.patch, PIG-953.patch
> Currently merge join implementation in pig includes construction of an index on sorted
data and use of that index to seek into the "right input" to efficiently perform the join
operation. Some loaders (notably the zebra loader) internally implement an index on sorted
data and can perform this seek efficiently using their index. So the use of the index needs
to be abstracted in such a way that when the loader supports indexing, pig uses it (indirectly
through the loader) and does not construct an index. 

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