John Omernik created DRILL-4460:
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Summary: Provide feature that allows fall back to sort aggregation
Key: DRILL-4460
URL: https://issues.apache.org/jira/browse/DRILL-4460
Project: Apache Drill
Issue Type: Improvement
Components: Execution - Flow
Affects Versions: 1.5.0
Reporter: John Omernik
Currently, the default setting for Drill is to use a Hash (in Memory) model for
aggregations (set by planner.enable_hashagg = true as default). This works
well, but it's memory dependent and an out of memory condition will cause a
query failure. At this point, a user can alter session set
`planner.enable_hashagg` = false and run the query again. If memory is a
challenge again, the sort based approach will spill to disk allowing the query
to complete (slower).
What I am requesting is a feature, that defaults to be off (so Drill default
behavior will be the same after this feature is added) that would allow a query
that tried hash aggregation and failed due to out of memory to restart the same
query with sort aggregation. Basically, allowing the query to succeed, it will
try hash first, then go to sort. This would make for a better user experience
in that the query would succeed. Perhaps a warning could be set for the user
that would allow them to understand that this occurred, so they could just go
to a sort based query by default in the future.
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