[Hive] union all queries broken - all kinds of problems

1. Map-only job : same input
Hangs because mapper tries to same open twice, and hadoop filesystem complains.

Fix: Only initialize once - keep state at the Operator level for the same. Should do same for Close.

2. Map-only job : different inputs
Loss of data due to rename.

Fix: change rename to move files to the directory.

3. Map-only job in subquery + RedSink: works currently

4. 2 variables: so 4 sub-cases

Number of sub-queries having map-reduce jobs. (1/2)
Operator after Union (RS/FS)

a. Number of sub-queries having map-reduce jobs. 1
Operator after Union: RS

Can be done in 2MR - really difficult with current infrastructure.
Should do with 3 MR jobs now - break on top of UNION.
Future optimization: move operators between Union and RS before Union.

b. Number of sub-queries having map-reduce jobs. 2
Operator after Union: RS

Needs 3MR - Should do with 3 MR jobs - break on top of UNION.
Future optimization: move operators between Union and RS before Union.

c. Number of sub-queries having map-reduce jobs. 1
Operator after Union: FS

Can be done in 1MR - really difficult with current infrastructure.
Can be easily done with 2 MR by removing UNION and cloning operators between Union and FS.
Should do with 3 MR jobs now - break on top of UNION.
Followup optimization: 2MR should be able to handle

d. Number of sub-queries having map-reduce jobs. 2
Operator after Union: FS

Can be easily done with 2 MR by removing UNION and cloning operators between Union and FS.
Should do with 3 MR jobs now - break on top of UNION.
Followup optimization: 2MR should be able to handle