In the Hive WebUI / Drilldown: the Show Query tab always displays "UNKNOWN."
If the user wants to see the query plan here, they should set configuration hive.log.explain.output to true. The user should be made aware of this option:
1) in WebUI / Drilldown / Show Query and
2) in HiveConf.java, line 2232.
This configuration's description reads:
"Whether to log explain output for every query
When enabled, will log EXPLAIN EXTENDED output for the query at INFO log4j log level."
this should be added:
"...and in the WebUI / Show Query tab."