[HIVE-19474] Decimal type should be casted as part of the CTAS or INSERT Clause.

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.1.0, 3.0.0
• Component/s: Druid integration
• Labels: druid
• Assignee: Slim Bouguerra
• Reporter: Slim Bouguerra
• Created: 09/May/18 03:20
• Updated: 27/Feb/24 22:23
• Resolved: 14/May/18 16:35

Description

HIVE-18569  introduced a runtime config variable to allow the indexing of Decimal as Double, this leads to kind of messy state, Hive metadata think the column is still decimal while it is stored as double. Since the Hive metadata of the column is Decimal the logical optimizer will not push down aggregates. i tried to fix this by adding some logic to the application but it makes the code very clumsy with lot of branches. Instead i propose to revert  HIVE-18569  and let the user introduce an explicit cast this will be better since the metada reflects actual storage type and push down aggregates will kick in and there is no config needed without adding any code or bug.

cc ashutoshc and nishantbangarwa

You can see the difference with the following DDL

create table test_base_table(`timecolumn` timestamp, `interval_marker` string, `num_l` DECIMAL(10,2));
insert into test_base_table values ('2015-03-08 00:00:00', 'i1-start', 4.5);
set hive.druid.approx.result=true;
CREATE TABLE druid_test_table
STORED BY 'org.apache.hadoop.hive.druid.DruidStorageHandler'
TBLPROPERTIES ("druid.segment.granularity" = "DAY")
AS
select cast(`timecolumn` as timestamp with local time zone) as `__time`, `interval_marker`, cast(`num_l` as double)
FROM test_base_table;
describe druid_test_table;
explain select sum(num_l), min(num_l) FROM druid_test_table;
CREATE TABLE druid_test_table_2
STORED BY 'org.apache.hadoop.hive.druid.DruidStorageHandler'
TBLPROPERTIES ("druid.segment.granularity" = "DAY")
AS
select cast(`timecolumn` as timestamp with local time zone) as `__time`, `interval_marker`, `num_l`
FROM test_base_table;
describe druid_test_table_2;
explain select sum(num_l), min(num_l) FROM druid_test_table_2;

 

 

Issue Links

• is caused by: HIVE-18569 Hive Druid indexing not dealing with decimals in correct way.