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From "Philip (flip) Kromer (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-859) Optimizer throw error on self-joins
Date Sun, 04 Jul 2010 10:12:50 GMT

    [ https://issues.apache.org/jira/browse/PIG-859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12885011#action_12885011
] 

Philip (flip) Kromer commented on PIG-859:
------------------------------------------

There are many use cases for a self join -- graph explorations especially. Would it work to
say something like

{code:sql|title=bfs.pig}
-- Enumerate paths of length two
Edges = LOAD 'a' AS (src, dest);
E2Paths = Join Edges AS InLinks BY dest, Edges AS Outlinks BY src;
{code}



> Optimizer throw error on self-joins
> -----------------------------------
>
>                 Key: PIG-859
>                 URL: https://issues.apache.org/jira/browse/PIG-859
>             Project: Pig
>          Issue Type: Bug
>          Components: impl
>    Affects Versions: 0.3.0
>            Reporter: Ashutosh Chauhan
>
> Doing self-join results in exception thrown by Optimizer. Consider the following query
> {code}
> grunt> A = load 'a';
> grunt> B = Join A by $0, A by $0;
> grunt> explain B;
> 2009-06-20 15:51:38,303 [main] ERROR org.apache.pig.tools.grunt.Grunt -
> ERROR 1094: Attempt to insert between two nodes that were not connected.
> Details at logfile: pig_1245538027026.log
> {code}
> Relevant stack-trace from log-file:
> {code}
> Caused by: org.apache.pig.impl.plan.optimizer.OptimizerException: ERROR
> 2047: Internal error. Unable to introduce split operators.
>         at
> org.apache.pig.impl.logicalLayer.optimizer.ImplicitSplitInserter.transform(ImplicitSplitInserter.java:163)
>         at
> org.apache.pig.impl.logicalLayer.optimizer.LogicalOptimizer.optimize(LogicalOptimizer.java:163)
>         at org.apache.pig.PigServer.compileLp(PigServer.java:844)
>         at org.apache.pig.PigServer.compileLp(PigServer.java:781)
>         at org.apache.pig.PigServer.getStorePlan(PigServer.java:723)
>         at org.apache.pig.PigServer.explain(PigServer.java:566)
>         ... 8 more
> Caused by: org.apache.pig.impl.plan.PlanException: ERROR 1094: Attempt
> to insert between two nodes that were not connected.
>         at
> org.apache.pig.impl.plan.OperatorPlan.doInsertBetween(OperatorPlan.java:500)
>         at
> org.apache.pig.impl.plan.OperatorPlan.insertBetween(OperatorPlan.java:480)
>         at
> org.apache.pig.impl.logicalLayer.optimizer.ImplicitSplitInserter.transform(ImplicitSplitInserter.java:139)
>         ... 13 more
> {code}
> A possible workaround is:
> {code}
> grunt> A = load 'a';
> grunt> B = load 'a';
> grunt> C = join A by $0, B by $0;
> grunt> explain C;
> {code}

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