Miklos Szurap created HIVE-28970:
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             Summary: Support database and table names starting with underscore
                 Key: HIVE-28970
                 URL: https://issues.apache.org/jira/browse/HIVE-28970
             Project: Hive
          Issue Type: Bug
          Components: Hive, Query Planning, Tez
    Affects Versions: 4.0.1, 4.1.0
            Reporter: Miklos Szurap
         Attachments: insert_only_underscore_test.q

In HIVE-6431 it has been already raised that table names starting with 
underscore are not treated well. Some users also flagged that there is an 
inconsistent behavior how different tables are treated when the database name 
starts with the underscore character.
With some table types there are no results (zero rows) returned if the DB name 
starts with underscore.
Currently (as of 4.1.0-SNAPSHOT) this is the behavior for the select queries:
||Table type||db.tbl||db._tbl||_db.tbl||_db._tbl||
|ACID|OK|FAIL|OK|FAIL|
|Insert-only|OK|Zero rows|Zero rows|Zero rows|
|External|OK|FAIL|OK|FAIL|

FAIL - The select query fails with the "Input path does not exist" error 
message reported on HIVE-6431.

The insert goes through fine in all situations, the data is there, Impala can 
read these tables properly.

This became visible as some workloads were running on top of insert-only table 
with *_db.tbl* pattern, and in some earlier versions it was working fine but 
broke after some fix. (I did not investigate exactly which one)

Attached a query file for testing this: [^insert_only_underscore_test.q]



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