Affects Version/s: 0.98.0, 0.96.1.1
Release Note:My local site run generates the docbook correctly, looks good to me on both branches. I've committed this to 0.98 and trunk.
(Jimmy has been working on this one internally. I'm just the messenger raising this critical issue upstream).
So, if you make job jar and bundle up hbase inside in it because you want to access hbase from your mapreduce task, the deploy of the job jar to the cluster fails with:
So, ZCLBS is a hack. This class is in the hbase-protocol module. It is "in" the com.google.protobuf package. All is well and good usually.
But when we make a job jar and bundle up hbase inside it, our 'trick' breaks. RunJar makes a new class loader to run the job jar. This URLCLassLoader 'attaches' all the jars and classes that are in jobjar so they can be found when it does to do a lookup only Classloaders work by always delegating to their parent first (unless you are a WAR file in a container where delegation is 'off' for the most part) and in this case, the parent classloader will have access to a pb jar since pb is in the hadoop CLASSPATH. So, the parent loads the pb classes.
We then load ZCLBS only this is done in the claslsloader made by RunJar; ZKCLBS has a different classloader from its superclass and we get the above IllegalAccessError.
Now (Jimmy's work comes in here), this can't be fixed by reflection – you can't setAccess on a 'Class' – and though it probably could be fixed by hacking RunJar so it was somehow made configurable so we could put in place our own ClassLoader to do something like containers do for WAR files (probably not a bad idea), there would be some fierce hackery involved and besides, this won't show up in hadoop anytime too soon leaving hadoop 2.2ers out in the cold.
So, the alternatives are:
1. Undo the ZCLSB hack. We'd lose a lot of nice perf improvement but I'd say this is preferable to crazy CLASSPATH hacks.
2. Require folks put hbase-protocol – thats all you'd need – on the hadoop CLASSPATH. This is kinda crazy.
3. We could try shading the pb jar content or probably better, just pull pb into hbase altogether only under a different package. If it was in our code base, we could do more ZCLSB-like speedups.
I was going to experiment with #3 above unless anyone else has a better idea.