Verifing use of a query rewrite

You can use Apache Hive explain logging to check that a materialized view used a query rewrite.

By default explain logging is set to false in CDP.
  1. In Cloudera Manager, enable explain logging: Navigate to Clusters > HIVE_ON_TEZ-1 > Configuration, search for hive.log.explain.output, check HiveServer2 Default Group, and click Save Changes.
  2. Verify that the query rewrite used the materialized view by running an extended EXPLAIN statement:
    EXPLAIN EXTENDED SELECT empid, deptname
                            FROM emps
                            JOIN depts
                            ON (emps.deptno = depts.deptno)
                            WHERE hire_date >= '2017-01-01'
                            AND hire_date <= '2019-01-01';
    The output shows the alias default.mv1 for the materialized view in the TableScan section of the plan.
    OPTIMIZED SQL: SELECT `empid`, `deptname`          
                            FROM `default`.`mv1`                               
                            WHERE TIMESTAMP '2019-01-01 00:00:00.000000000' >= `hire_date` 
                            STAGE DEPENDENCIES:                                
                            Stage-0 is a root stage                          
                            STAGE PLANS:                                       
                            Stage: Stage-0                                   
                            Fetch Operator                                 
                            limit: -1                                    
                            Processor Tree:                              
                            alias: default.mv1                       
                            filterExpr: (hire_date <= TIMESTAMP'2019-01-01 
                            00:00:00') (type: boolean) |
                            GatherStats: false                       
                            Filter Operator                          
                            isSamplingPred: false                  
                            predicate: (hire_date <= TIMESTAMP'2019-01-01 
                            00:00:00') (type: boolean) 
                            Select Operator                        
                            expressions: empid (type: int), deptname (type: varchar(256)) 
                            outputColumnNames: _col0, _col1