[IMPALA-10197] Add KUDU_REPLICA_SELECTION config and query option

• Type: Improvement
• Status: Resolved
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: Impala 4.0.0
• Fix Version/s: Impala 4.1.0
• Component/s: Frontend
• Labels: kudu newbie ramp-up
• Epic Color: ghx-label-3
• Assignee: Wenzhe Zhou
• Reporter: Grant Henke
• Created: 29/Sep/20 14:38
• Updated: 03/Jun/21 07:42
• Resolved: 24/May/21 15:12

Description

Sometimes it is useful to target queries at the LEADER_ONLY instead of the default CLOSEST_REPLICA. We should expose this option in Impala similar to the way KUDU_READ_MODE is exposed:
https://impala.apache.org/docs/build/html/topics/impala_kudu_read_mode.html

Currently there is a test only flag, FLAGS_pick_only_leaders_for_tests, that somewhat does this:
https://github.com/apache/impala/blob/da2999afd9ddc45d35141649d17db507e03ee9bf/be/src/exec/kudu-scanner.cc#L195-L198

Issue Links

• is related to: IMPALA-10481 Lack of TServer affinity in remote Kudu scans results in bad OS buffer cache behavior on tablet servers