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From Christian Decker <decker.christ...@gmail.com>
Subject Re: Cassandra and Pig
Date Fri, 13 Aug 2010 17:16:26 GMT
Wow, that was extremely quick, thanks Stu :-)
I'm still a bit unclear on what the pig_cassandra script does. It sets some
variables (PIG_CLASSPATH for one) and then starts the original pig binary
but injects some libraries in it (libthrift and pig-core) but strangely not
the cassandra loadfunc, why not?

Anyway now I understand why I was getting different errors when executing
directly via Pig compared to through pig_cassandra. Still I get an exception
which I cannot explain where it comes from (http://pastebin.com/JYfSSfny):

Caused by: java.lang.RuntimeException: Could not resolve error that occured
when launching map reduce job: java.lang.ExceptionInInitializerError
 at
org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher$JobControlThreadExceptionHandler.uncaughtException(MapReduceLauncher.java:510)
 at java.lang.Thread.dispatchUncaughtException(Thread.java:1845)


Any idea? Thanks again for your fast answer :)

On Fri, Aug 13, 2010 at 6:55 PM, Stu Hood <stu.hood@rackspace.com> wrote:

> That error is coming from the frontend: the jars must also be on the local
> classpath. Take a look at how contrib/pig/bin/pig_cassandra sets up
> $PIG_CLASSPATH.
>
> -----Original Message-----
> From: "Christian Decker" <decker.christian@gmail.com>
> Sent: Friday, August 13, 2010 11:30am
> To: user@cassandra.apache.org
> Subject: Cassandra and Pig
>
> Hi all,
>
> I'm trying to get Pig to read data from a Cassandra cluster, which I
> thought
> trivial since Cassandra already provides me with the CassandraStorage
> class.
> Problem is that once I try executing a simple script like this:
>
> register /path/to/pig-0.7.0-core.jar;register
> /path/to/libthrift-r917130.jar;
> register /path/to/cassandra_loadfunc.jarrows = LOAD
> 'cassandra://Keyspace1/Standard1' USING
> org.apache.cassandra.hadoop.pig.CassandraStorage();cols = FOREACH rows
> GENERATE flatten($1);colnames = FOREACH cols GENERATE $0;namegroups =
> GROUP colnames BY $0;namecounts = FOREACH namegroups GENERATE
> COUNT($1), group;orderednames = ORDER namecounts BY $0;topnames =
> LIMIT orderednames 50;dump topnames;
>
> I just end up with a NoClassDefFoundError:
>
> ERROR org.apache.pig.tools.grunt.Grunt -
> org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1066: Unable to
> open iterator for alias topnames
> at org.apache.pig.PigServer.openIterator(PigServer.java:521)
>  at
> org.apache.pig.tools.grunt.GruntParser.processDump(GruntParser.java:544)
> at
>
> org.apache.pig.tools.pigscript.parser.PigScriptParser.parse(PigScriptParser.java:241)
>  at
>
> org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:162)
> at
>
> org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:138)
>  at org.apache.pig.tools.grunt.Grunt.exec(Grunt.java:89)
> at org.apache.pig.Main.main(Main.java:391)
> Caused by: org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1002:
> Unable to store alias topnames
>  at org.apache.pig.PigServer.store(PigServer.java:577)
> at org.apache.pig.PigServer.openIterator(PigServer.java:504)
>  ... 6 more
> Caused by: org.apache.pig.backend.executionengine.ExecException: ERROR
> 2117:
> Unexpected error when launching map reduce job.
> at
>
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher.launchPig(MapReduceLauncher.java:209)
>  at
>
> org.apache.pig.backend.hadoop.executionengine.HExecutionEngine.execute(HExecutionEngine.java:308)
> at org.apache.pig.PigServer.executeCompiledLogicalPlan(PigServer.java:835)
>  at org.apache.pig.PigServer.store(PigServer.java:569)
> ... 7 more
> Caused by: java.lang.RuntimeException: Could not resolve error that occured
> when launching map reduce job: java.lang.NoClassDefFoundError:
> org/apache/thrift/TBase
>  at
>
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher$JobControlThreadExceptionHandler.uncaughtException(MapReduceLauncher.java:510)
>  at java.lang.Thread.dispatchUncaughtException(Thread.java:1845)
>
> I cannot think of a reason as to why. As far as I understood it Pig takes
> the jar files in the script, unpackages them, creates the execution plan
> for
> the script itself and then bundles it into a single jar again, then submits
> it to the HDFS from where it will be executed in Hadoop, right?
> I also checked that the class in question actually is in the libthrift jar,
> so what's going wrong?
>
> Regards,
> Chris
>
>
>

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