[HIVE-8485] HMS on Oracle incompatibility

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.0.0
• Component/s: Metastore

Environment

Oracle as metastore DB

Release Note

Introduces a new hive-site.xml parameter : "hive.metastore.orm.retrieveMapNullsAsEmptyStrings" that defaults to false.
For operation with oracle, or any other datastore that converts empty strings to nulls, users should set this to true.

If this parameter is set to true, ObjectStore will transform any null map values it finds in any of the parameters maps to "".
If this parameter is set to false, ObjectStore will prune any map entry where the value is null.

• Assignee: Sushanth Sowmyan
• Reporter: Ryan Pridgeon
• Created: 16/Oct/14 12:59
• Updated: 03/Apr/18 11:15
• Resolved: 26/Jan/15 23:23

Description

Oracle does not distinguish between empty strings and NULL,which proves problematic for DataNucleus.
In the event a user creates a table with some property stored as an empty string the table will no longer be accessible.
i.e. TBLPROPERTIES ('serialization.null.format'='')
If they try to select, describe, drop, etc the client prints the following exception.
ERROR ql.Driver: FAILED: SemanticException [Error 10001]: Table not found <table name>
The work around for this was to go into the hive metastore on the Oracle database and replace NULL with some other string. Users could then drop the tables or alter their data to use the new null format they just set.

Issue Links

• is duplicated by: HIVE-14116 TBLPROPERTIES does not allow empty string values when Metastore is backed by Oracle database.
• relates to: HIVE-12476 Metastore NPE on Oracle with Direct SQL