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From "Liu, Ming (HPIT-GADSC)" <ming.l...@hp.com>
Subject how to use RegionCoprocessorEnvironment getSharedData() to share data among coprocessors?
Date Wed, 15 Apr 2015 05:35:12 GMT
Hi, all,

I am trying to learn how to share data between two coprocessors. I have one Observer coprocessor
and one Endpoint coprocessor. In the observer, it overload the prePut/preDelete to maintain
a counter. And I want the Endpoint coprocessor to read that counter and return to client caller.
So I want to use the getSharedData() method in RegionCoprocessorEnvironment, but I cannot
make it work. Could anybody help me here?

In the Observer Coprocessor :
During start(), create the shared object "counter":
-----------------------------------------------------------------
public void start(CoprocessorEnvironment envi) throws IOException {
  Env.getSharedData().put("counter", new Long(0) ); //create the counter
-----------------------------------------------------------------

In the Endpoint coprocessor:
During start(), try to read the shared "counter" , but failed.
------------------------------------------------------------------
public void start(CoprocessorEnvironment envi) throws IOException {
     LOG.info("The size of sharedData map is: " + envi.getSharedData().size() ); //try to
get the counter
------------------------------------------------------------------
Here it print 0, if I use evni.getSharedData().containsKey("counter"), it will return false.

When creating table, I call addCoprocessor() method to add Observer first, then Endpoint coprocessor.
I confirmed that by checking the hbase log file message. I only have one region for that table
during the run. I confirmed by hbase shell status 'detailed' command.

There is not much example I can find about how to use getSharedData(), could someone help
me here? What is missing in my simple code? Thanks very much in advance!

Thanks,
Ming

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