Kunal Khatua created DRILL-5715:
-----------------------------------

             Summary: Performance of refactored HashAgg operator regressed
                 Key: DRILL-5715
                 URL: https://issues.apache.org/jira/browse/DRILL-5715
             Project: Apache Drill
          Issue Type: Bug
          Components: Execution - Codegen
    Affects Versions: 1.11.0
         Environment: 10-node RHEL 6.4 (32 Core, 256GB RAM)
            Reporter: Kunal Khatua
            Assignee: Boaz Ben-Zvi
             Fix For: 1.12.0


When running the following simple HashAgg-based query on a TPCH-table - 
Lineitem with 6Billion rows on a 10 node setup (with a single partition to 
disable any possible spilling to disk)

{code:sql}
select count(*) 
from (
  select l_quantity
    , count(l_orderkey) 
  from lineitem 
  group by l_quantity 
)  {code}

the runtime increased from {{7.378 sec}} to {{11.323 sec}} [reported by the 
JDBC client].

To disable spill-to-disk in Drill-1.11.0, the {{drill-override.conf}} was 
modified to 
{code}drill.exec.hashagg.num_partitions : 1{code}

Attached are two profiles
Drill 1.10.0 : 2675cc73-9481-16e0-7d21-5f1338611e5f.sys.drill 
Drill 1.11.0 : 2675de42-3789-47b8-29e8-c5077af136db.sys.drill 

A separate run was done for both scenarios with the 
{{planner.width.max_per_node=10}} and profiled with YourKit.

Image snippets are attached, indicating the hotspots in both builds:
Drill 1.10.0 : 
 Profile: 26736242-d084-6604-aac9-927e729da755.sys.drill
 HotSpot: drill-1.10.0_hotspot.jpg 
Drill 1.11.0 : 
 Profile: 26736615-9e86-dac9-ad77-b022fd791f67.sys.drill
 HotSpot: drill-1.11.0_hotspot.jpg 




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