Mixed version clusters
A query to a mixed version cluster may miss records while upgrading from server 5.6 and earlier to 5.7 and later. The fail-on-cluster-change flag will not work in this case as some records could be missed even after migrations complete.
During the rolling upgrade, this issue will not manifest if the set of nodes remains the same and the (delta) migrations settle down. When the cluster goes to n-1 nodes and the (delta) migrations complete, the query may miss some records because a new node changed the partition distribution. This is due to the replica write wire protocol change causing older versions of Aerospike to not update the secondary index on the non-master replicas. When the non-master replicas on the receiving end of replica writes from upgraded nodes do get promoted to master, some records could be missed. This can happen if upgraded nodes unexpectedly leave the cluster, while a node is stopped during maintenance or if node ids change during the upgrade process.
For more information about server 5.7, see the Release Notes.