tree d6e90c72d60ecc3f6ae3d389f5fceab37c95d5f4
parent a1588e44980c648cb7f9263cbd0409abfbaeacf7
author Lars Volker <lv@cloudera.com> 1573582419 -0800
committer Impala Public Jenkins <impala-public-jenkins@cloudera.com> 1575420004 +0000

IMPALA-9151: Maintain cluster size in ExecutorMembershipSnapshot

This change improves the cluster membership snapshot we maintain in the
frontend in cases where all executors have been shut down or none have
started yet.

Prior to this change when configuring Impala with executor groups, the
planner might see a ExecutorMembershipSnapshot that has no executors in
it. This could happen if the first executor group had not started up
yet, or if all executor groups had been shutdown. If this happened, the
planner would make sub-optimal decisions, e.g. decide on a broadcast
join vs a partitioned hash join.

With this change if no executors have been registered so far, the
planner will use the expected number of executors which can be set using
the -num_expected_executors flag and is 20 by default. After executors
come online, the planner will use the size of the largest healthy
executor group, and it will hold on to the group's size even if it shuts
down or becomes unhealthy. This allows the planner to work on the
assumption that a healthy executor group of the same size will
eventually come online to execute the query.

Change-Id: Ib6b05326c82fb3ca625c015cfcdc38f891f5d4f9
Reviewed-on: http://gerrit.cloudera.org:8080/14756
Reviewed-by: Lars Volker <lv@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>