[IMPALA-5713] Consider always reserving memory for grouping pre-aggregations

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 2.10.0
• Fix Version/s: Impala 2.10.0
• Component/s: Backend
• Labels: resource-management
• Target Version: Impala 2.10.0
• Epic Color: ghx-label-3
• Assignee: Tim Armstrong
• Reporter: Tim Armstrong
• Created: 24/Jul/17 23:05
• Updated: 25/Aug/17 00:53
• Resolved: 25/Aug/17 00:53

Description

The initial IMPALA-3200 code added the ability for a grouping pre-aggregation to run with zero reservation, passing through all of the rows. However, this is a very low performance mode for aggregations that reduce their input a lot, since it forces everything to be sent over the network. We would be better off in most cases requiring more memory but not allowing perf to degrade so much.

Issue Links

• is related to: IMPALA-5710 Stress test is not aware of aggregation passthrough under memory pressure