[IMPALA-13191] Do Not Create Sort Node with Constant Ordering Expression

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: fe, Frontend
• Labels: performance
• Epic Color: ghx-label-14
• Assignee: Unassigned
• Reporter: Noemi Pap-Takacs
• Created: 6 days ago 14:34
• Updated: 6 days ago 15:42

Description

Rows are sorted before inserting into partitioned Iceberg tables. See Planner.createPreDmlSort().
If we update the partitioning column of the table, the sort ordering expression will be the partition column. If we set the new value to a constant (writing only to 1 partition), it will be evaluated as a constant. Therefore the Sort Node will get a constant ordering expression and works unnecessarily ordering indistinct values.
For example:

create table ice_part partitioned by spec (l_discount) stored by iceberg tblproperties('format-version'='2') as select * from tpch_parquet.lineitem where l_linenumber=1;
explain update ice_part set l_discount=0.11 where l_discount>0.07;

The output of explain - the plan - contains a Sort Node with the following ordering expression:

04:SORT
|  order by: 0.11 ASC NULLS LAST

It is unnecessary to create a Sort Node to sort rows by a constant ordering expression. Constant expressions should be omitted, just like empty ones.