PHOENIX-6671 Avoid ShortCirtuation Coprocessor Connection with HBase 2.x

[lhofhansl]

From Jira: See PHOENIX-6501, PHOENIX-6458, and HBASE-26812.

HBase's ShortCircuit Connection are fundamentally broken in HBase 2. We might be able to fix it there, but with all the work the RPC handlers perform now (closing scanning, resolving current user, etc), I doubt we'll get that 100% right. HBase 3 has removed this functionality.

Even with HBase 2, which does not have the async protobuf code, I could hardly see any performance improvement from circumventing the RPC stack in case the target of a Get or Scan is local. Even in the most ideal conditions where everything is local, there was improvement outside of noise.

I suggest we do not use ShortCircuited Connections in Phoenix 5+.

[lhofhansl]

Seems that I cannot look at the output of the test run...?

Update: I can now. Time out in BasePermissionsIT:812 (Where it creates an index), so it might be related.

[stoty]

Closing as the corresponding ticket is closed. (This is fixed in PHOENIX-6874)