[IMPALA-9765] Preaggregations should stop expanding if memory is scarce

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Backend
• Labels: resource-management
• Target Version: Product Backlog
• Epic Color: ghx-label-8
• Assignee: Unassigned
• Reporter: Tim Armstrong
• Created: 20/May/20 16:45
• Updated: 20/May/20 20:22

Description

We've seen several workloads recently where the preaggregations expanded to consume nearly all of the memory reservation on a host, starving the merge agg. We should think about runtime mechanisms to reduce the impact of this, e.g. stop expanding once we are low on memory.

I think we'd need to do this based on reservation_limit_ - child_reservations_ - used_reservation_ on the query mem tracker. Various heuristics are possible. Even something simple like keeping 10-20% free would be beneficial.

Related: IMPALA-2945 IMPALA-9530 IMPALA-9591

Issue Links

• relates to: IMPALA-2945 Pre-aggregation cardinality estimates do not take into account data distribution
• relates to: IMPALA-9591 Automatically cap pre-aggregation memory consumption to match estimate
• relates to: IMPALA-9530 Allow limiting memory consumed by preaggregation