[HIVE-14302] Tez: Optimized Hashtable can support DECIMAL keys of same precision

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.2.0
• Fix Version/s: 4.0.0-alpha-1
• Component/s: Tez
• Labels: pull-request-available
• Assignee: Mustafa İman
• Reporter: Gopal Vijayaraghavan
• Created: 21/Jul/16 01:01
• Updated: 27/Feb/24 22:23
• Resolved: 11/Oct/19 16:58

Description

Decimal support in the optimized hashtable was decided on the basis of the fact that Decimal(10,1) == Decimal(10, 2) when both contain "1.0" and "1.00".

However, the joins now don't have any issues with decimal precision because they cast to common.

create temporary table x (a decimal(10,2), b decimal(10,1)) stored as orc;
insert into x values (1.0, 1.0);

    > explain logical select count(1) from x, x x1 where x.a = x1.b;
OK  
LOGICAL PLAN:
$hdt$_0:$hdt$_0:x
  TableScan (TS_0)
    alias: x
    filterExpr: (a is not null and true) (type: boolean)
    Filter Operator (FIL_18)
      predicate: (a is not null and true) (type: boolean)
      Select Operator (SEL_2)
        expressions: a (type: decimal(10,2))
        outputColumnNames: _col0
        Reduce Output Operator (RS_6)
          key expressions: _col0 (type: decimal(11,2))
          sort order: +
          Map-reduce partition columns: _col0 (type: decimal(11,2))
          Join Operator (JOIN_8)
            condition map:
                 Inner Join 0 to 1
            keys:
              0 _col0 (type: decimal(11,2))
              1 _col0 (type: decimal(11,2))
            Group By Operator (GBY_11)
              aggregations: count(1)
              mode: hash
              outputColumnNames: _col0

See cast up to Decimal(11, 2) in the plan, which normalizes both sides of the join to be able to compare HiveDecimal as-is.

Issue Links

• links to: GitHub Pull Request #803