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https://issues.apache.org/jira/browse/PIG-1309?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ashutosh Chauhan updated PIG-1309:
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Release Note:
With this patch, it is now possible to perform map-side cogroup if data is
sorted and loader implements certain interfaces. Primary algorithm is based on
sort-merge join with additional restrictions.
Following preconditions must be met to use this feature:
1) No other operations can be done between load and join statements.
2) Data must be sorted on join keys for all tables in ASC order.
3) Nulls are considered smaller then everything. So, if data contains null
keys, they should occur before anything else.
4) Left-most loader must implement {CollectableLoader} interface as well as
{OrderedLoadFunc}.
5) All other loaders must implement IndexableLoadFunc.
6) Type information must be provided in schema for all the loaders.
Note that Zebra loader satisfies all of these conditions, so can be used out of
box.
Similar conditions apply to map-side outer joins (using merge) (PIG-1353) as
well.
Example:
A = load 'data1' using org.apache.hadoop.zebra.pig.TableLoader('id:int',
'sorted');
B = load 'data2' using org.apache.hadoop.zebra.pig.TableLoader('id:int',
'sorted');
C = COGROUP A by id, B by id using 'merge';
was:
With this patch, it is now possible to perform map-side cogroup if data is
sorted and one of the loader implements {{CollectableLoader}} interface.
Primary algorithm is based on sort-merge join.
Additional implementation details:
1) No other operations can be done between load and join statements.
2) Data must be sorted in ASC order.
3) Nulls are considered smaller then everything. So, if data contains null
keys, they should occur before anything else.
4) Left-most loader must implement CollectableLoader interface as well as
OrderedLoadFunc.
5) All other loaders must implement IndexableLoadFunc.
Note that Zebra loader satisfies all of these conditions, so can be used out of
box.
Similiar conditions apply to map-side cogroups (PIG-1309) as well.
Example:
A = load 'data1' using org.apache.hadoop.zebra.pig.TableLoader('', 'sorted');
B = load 'data2' using org.apache.hadoop.zebra.pig.TableLoader('', 'sorted');
C = COGROUP A by id, B by id using 'merge';
> Map-side Cogroup
> ----------------
>
> Key: PIG-1309
> URL: https://issues.apache.org/jira/browse/PIG-1309
> Project: Pig
> Issue Type: Bug
> Components: impl
> Reporter: Ashutosh Chauhan
> Assignee: Ashutosh Chauhan
> Fix For: 0.7.0, 0.8.0
>
> Attachments: mapsideCogrp.patch, pig-1309_1.patch, pig-1309_2.patch,
> PIG_1309_7.patch
>
>
> In never ending quest to make Pig go faster, we want to parallelize as many
> relational operations as possible. Its already possible to do Group-by(
> PIG-984 ) and Joins( PIG-845 , PIG-554 ) purely in map-side in Pig. This jira
> is to add map-side implementation of Cogroup in Pig. Details to follow.
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