[jira] [Created] (DRILL-5737) Hash Agg uses more than the allocated memory under certain low memory conditions

["Sorabh Hamirwasia (JIRA)" <ji...@apache.org>]

Sorabh Hamirwasia created DRILL-5737:
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             Summary: Hash Agg uses more than the allocated memory under certain low memory conditions
                 Key: DRILL-5737
                 URL: https://issues.apache.org/jira/browse/DRILL-5737
             Project: Apache Drill
          Issue Type: Bug
            Reporter: Sorabh Hamirwasia


Reported by [~rkins]

Based on the memory computations drill thinks that there is not sufficient memory and falls back to a single partition case. The single partition case however does not respect the memory constraints imposed and completes the query using ~130MB of memory

{code:java}
alter session set `planner.width.max_per_node` = 1;
alter session set `planner.memory.max_query_memory_per_node` = 117127360;
select count(*) from (select max(nulls_col), max(length(nulls_col)), max(`filename`) from dfs.`/drill/testdata/hash-agg/data1` group by no_nulls_col) d;
{code}

Based on analysis by [~ben-zvi] this is by design. When the Hash Aggr Op finds that there is not enough memory for at least two partitions, it falls back to the pre 1.11 behavior ( using 10GB limit ). 

Solution is to provide a configuration based on which the fallback will be either allowed or query will be failed.



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