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 from 0.18, 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.

Bug fixes:

• MapperParsingException on percolation with _size enabled (#2352)
• Aliases API times out when actions end up with no actual change to aliases (#2345)
• Highlighting fails for ConstantScoreQuery (#2332)
• Setting index_analyzer incorrectly sets analyzer (#2329)
• Mapping: Using default mapping type with _source excludes (or array based config) can cause the array to grow indefinitely (#2317)
• With cache turned off I’m getting the following error: nested: ClassCastException[org.apache.lucene.util.FixedBitSet cannot be cast to org.elasticsearch.common.lucene.docset.FixedBitDocSet] (#2340)