hive on Tez - merging orc files

[patcharee]

Hi,

Is there anyone using hortonworks sandbox 2.2? I am trying to use hive 
on Tez on the sandbox. I set the running engine in hive-site.xml to Tez.

    <property>
      <name>hive.execution.engine</name>
      <value>tez</value>
    </property>

Then I ran the script that alters a table to merge small orc files 
(alter table orc_merge5a partition(st=0.8) concatenate;). The merging 
feature worked, but Hive does not use Tez, it used MapReduce, so weird!

Another point, I tried to run the same script on the production cluster 
which is on always Tez, the merging feature sometimes worked, sometimes 
did not.

I would appreciate any suggestions.

BR,
Patcharee