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https://issues.apache.org/jira/browse/HBASE-15686?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15253331#comment-15253331
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Jerry He commented on HBASE-15686:
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Hi, [~sjlee0]
Thanks for the explanation.
I am neutral on creating a configurable co-processor class exempt mechanism.

> unable to dynamically load a table coprocessor if it belongs in 
> org.apache.hadoop
> ---------------------------------------------------------------------------------
>
>                 Key: HBASE-15686
>                 URL: https://issues.apache.org/jira/browse/HBASE-15686
>             Project: HBase
>          Issue Type: Bug
>          Components: Coprocessors
>    Affects Versions: 1.0.1
>            Reporter: Sangjin Lee
>         Attachments: 15686.wip
>
>
> As part of Hadoop's Timeline Service v.2 (YARN-2928), we're adding a table 
> coprocessor (YARN-4062). However, we're finding that the coprocessor cannot 
> be loaded dynamically. A relevant snippet for the exception:
> {noformat}
> java.io.IOException: Class 
> org.apache.hadoop.yarn.server.timelineservice.storage.flow.FlowRunCoprocessor 
> cannot be loaded
>     at 
> org.apache.hadoop.hbase.master.HMaster.sanityCheckTableDescriptor(HMaster.java:1329)
>     at org.apache.hadoop.hbase.master.HMaster.createTable(HMaster.java:1269)
>     at 
> org.apache.hadoop.hbase.master.MasterRpcServices.createTable(MasterRpcServices.java:398)
>     at 
> org.apache.hadoop.hbase.protobuf.generated.MasterProtos$MasterService$2.callBlockingMethod(MasterProtos.java:42436)
>     at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2031)
>     at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:107)
>     at 
> org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:130)
>     at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:107)
>     at java.lang.Thread.run(Thread.java:745)
> Caused by: java.io.IOException: Class 
> org.apache.hadoop.yarn.server.timelineservice.storage.flow.FlowRunCoprocessor 
> cannot be loaded
>     at 
> org.apache.hadoop.hbase.regionserver.RegionCoprocessorHost.testTableCoprocessorAttrs(RegionCoprocessorHost.java:324)
>     at 
> org.apache.hadoop.hbase.master.HMaster.checkClassLoading(HMaster.java:1483)
>     at 
> org.apache.hadoop.hbase.master.HMaster.sanityCheckTableDescriptor(HMaster.java:1327)
>     ... 8 more
> Caused by: java.lang.ClassNotFoundException: 
> org.apache.hadoop.yarn.server.timelineservice.storage.flow.FlowRunCoprocessor
>     at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
>     at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
>     at java.security.AccessController.doPrivileged(Native Method)
>     at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
>     at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
>     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
>     at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
>     at 
> org.apache.hadoop.hbase.util.CoprocessorClassLoader.loadClass(CoprocessorClassLoader.java:275)
>     at 
> org.apache.hadoop.hbase.regionserver.RegionCoprocessorHost.testTableCoprocessorAttrs(RegionCoprocessorHost.java:322)
>     ... 10 more
> {noformat}
> We tracked it down to the fact that {{CoprocessorClassLoader}} regarding all 
> hadoop classes as exempt from loading from the coprocessor jar. Since our 
> coprocessor sits in the coprocessor jar, and yet the loading of this class is 
> delegated to the parent which does not have this jar, the classloading fails.
> What would be nice is the ability to exclude certain classes from the exempt 
> classes so that they can be loaded via table coprocessor classloader. See 
> hadoop's {{ApplicationClassLoader}} for a similar feature.
> Is there any other way to load this coprocessor at the table scope?



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