[IMPALA-9221] Optimize HashRing's map implementation

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: Impala 3.4.0
• Component/s: Backend
• Epic Color: ghx-label-2
• Assignee: Michael Smith
• Reporter: Joe McDonnell
• Created: 07/Dec/19 00:25
• Updated: 26/May/22 20:56
• Resolved: 26/May/22 20:56

Description

The hash ring used for consistent scheduling currently uses a std::map for the hash-to-IpAddr lookup. HashRing is heavy on reads, with writes only happening when executors come and go. There are some cases where we copy the HashRing.

The standard map uses a large number of small allocations. This hurts cache performance, adds overhead, and also increases the cost of copying the structure. Something like boost's flat_map or Abseil's btree_map is likely to be more efficient.