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From "Xu Zhang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-72) Porting Pig unit tests to use MiniDFSCluster and MiniMRCluster on the local machine
Date Wed, 20 Feb 2008 22:49:43 GMT

    [ https://issues.apache.org/jira/browse/PIG-72?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12570869#action_12570869

Xu Zhang commented on PIG-72:

Exceptions like the following happen with the recent Pig revisions. 

      Caused an  ERROR
java.io.IOException cannot be cast to   java.lang.Error
java.lang.ClassCastException: java.io.IOException  cannot be  cast to  java.lang.Error
        at   org.apache.pig.impl.logicalLayer.parser.QueryParser.LoadClause(QueryParser.java:646)
        at   org.apache.pig.impl.logicalLayer.parser.QueryParser.BaseExpr(QueryParser.java:495)
        at   org.apache.pig.impl.logicalLayer.parser.QueryParser.NestedExpr(QueryParser.java:423)
        at   org.apache.pig.impl.logicalLayer.parser.QueryParser.ForEachClause(QueryParser.java:1348)
        at   org.apache.pig.impl.logicalLayer.parser.QueryParser.BaseExpr(QueryParser.java:550)
        at   org.apache.pig.impl.logicalLayer.parser.QueryParser.Expr(QueryParser.java:371)
        at   org.apache.pig.impl.logicalLayer.parser.QueryParser.Parse(QueryParser.java:227)
        at   org.apache.pig.impl.logicalLayer.LogicalPlanBuilder.parse(LogicalPlanBuilder.java:47)
        at   org.apache.pig.PigServer.registerQuery(PigServer.java:228)
        at   org.apache.pig.test.TestInfixArithmetic.testSubtract(TestInfixArithmetic.java:71)

The exceptions occur in this scenario: The 1st test method that calls registerQuery() will
pass,  but the subsequent test method(s) that call registerQuery() will get this kind of exception.
 For  example,

    //  The 1st test method that calls registerQuery() will pass  with no  exception
    public void testSimpleCount()   throws Throwable   {
        PigServer pig =  new   PigServer("mapreduce");

    //   The 2nd and following test methods that call registerQuery() will get  the  exception
    public void testGroupCount()  throws  Throwable  {
        PigServer pig =   new   PigServer("mapreduce");


On line 646 of QueryParser.java, the program tries to cast an IOException into an Error which
generates this exception.  This exception did not occur with the earlier revisions of Pig.
 Does anyone have any idea what the root cause is for this kind of exceptions and how to avoid

> Porting Pig unit tests to use MiniDFSCluster and MiniMRCluster on the local machine
> -----------------------------------------------------------------------------------
>                 Key: PIG-72
>                 URL: https://issues.apache.org/jira/browse/PIG-72
>             Project: Pig
>          Issue Type: Test
>          Components: tools
>            Reporter: Xu Zhang
>         Attachments: hadoop-0.15.3-dev-test-utils.jar, PortPigUnitTestToMiniClusters.patch,
> We have the need to port the Pig unit tests to use MiniDFSCluster and MiniMRCluster,
so that tests can be executed with the DFS and MR threads on the local machine.   This feature
will eliminate the need to set up a real distributed hadoop cluster before running the unit
tests, as everything will now be carried out with the (mini) cluster on the user's local machine.
> One prerequisite for using this feature is a hadoop jar that has the class files for
MiniDFSCluster, MiniMRCluster and other supporting components.  I have been able to generate
such a jar file with a special target added by myself to hadoop's build.xml and have also
logged a hadoop jira to request this target be a permanent part of that build file.  If possible,
we can just replace hadoop15.jar with this jar file on the SVN source tree and then the users
will never need to worry about the availability of this jar file. Please find such a hadoop
jar file in the attachment.
> To use the feature in unit tests, the user just need to call MiniClusterBuilder.buildCluster()
before a PigServer instance is created with the string "mapreduce" as the parameter to its
constructor.  Here is an example of how the MiniClusterBuilder is used in a test case class:
>         public class TestWhatEver extends TestCase {
> 	        private String initString = "mapreduce";
> 	        private MiniClusterBuilder cluster = MiniClusterBuilder.buildCluster();
>                 @Test
>                 public void testGroupCountWithMultipleFields() throws Exception {
>                         PigServer pig = new PigServer(initString);
>                         // Do something with the pig server, such as registering and
executing Pig 
>                         // queries. The queries will executed with the local cluster.

>                 }
>                 // More test cases if needed
>         }
> To run the unit tests with the local cluster, under the top directory of the source tree,
issue the command "ant test". Notice that you do not need to specify the location of the hadoop-site.xml
file with the command line option "-Djunit.hadoop.conf=<dir>" anymore. 

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