Upgrade Notes:

• 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.

New features:

• Index Blocks: Add index.blocks.write, index.blocks.read, and index.blocks.metadata settings (#1771)

Enhancements:

• Add cache thread pool to handle cache loading of async caches (bloom filter) (#1777)
• Java API for require_field_match (#1795)
• Highlighting using the default highlighter (not using term vectors) only highlights on the first 50*1024 chars (#1796)
• Get: Add a specific get thread pool that handles get request (#1778)
• Query DSL: indices filter type (#1787)
• Scripting: Allow to disable dynamic script execution (#1763)

Bug fixes:

• Special host config notation _[interfaceName]_ might fail to resolve the host address (#1754)
• RemoteTransportException on _analyze request to specific index (#1770)
• Closing a shard can cause a search/stats request that tries to acquire a handle to search while its closing to spin (#1772)
• IOException when restricting fields and returning nested arrays. (#1774)
• mlt_field doesn’t support boost (#1773)
• When node.data is set to false, the upgrade shards process from 0.18 fails (#1793)
• Get/MultiGet API with no type provided and doc does not exists causes a failure (#1794)