Upgrading from 0.18 requires issuing a full flush of all the indices in the cluster (curl host:9200/_flush) before shutting down the cluster, with no indexing operations happening after the flush.
The local gateway state structure has changed, a backup of the state files is created when upgrading, they can then be used to downgrade back to 0.18. Don’t downgrade without using them.
Enhancements:
Use bloom filter when flushing (applying deletes) (#2058)
“index_analyzer” and “search_analyzer” should override “analyzer” (#2052)