[HIVE-4838] Refactor MapJoin HashMap code to improve testability and readability

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.12.0
• Assignee: Brock Noland Assign to me
• Reporter: Brock Noland
• Created: 10/Jul/13 17:02
• Updated: 15/Oct/13 23:29
• Resolved: 16/Aug/13 15:53

Description

MapJoin is an essential component for high performance joins in Hive and the current code has done great service for many years. However, the code is showing it's age and currently suffers from the following issues:

• Uses static state via the MapJoinMetaData class to pass serialization metadata to the Key, Row classes.
• The api of a logical "Table Container" is not defined and therefore it's unclear what apis HashMapWrapper
  needs to publicize. Additionally HashMapWrapper has many used public methods.
• HashMapWrapper contains logic to serialize, test memory bounds, and implement the table container. Ideally these logical units could be seperated
• HashTableSinkObjectCtx has unused fields and unused methods
• CommonJoinOperator and children use ArrayList on left hand side when only List is required
• There are unused classes MRU, DCLLItemm and classes which duplicate functionality MapJoinSingleKey and MapJoinDoubleKeys

Issue Links

• relates to: HIVE-4730 Join on more than 2^31 records on single reducer failed (wrong results)
• relates to: HIVE-5110 Investigate memory consumption during map-side join
• links to: Review