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:

• Store Throttling (node level and/or index level) with options on merge or all (#2041)
• Stored Fields Compression (#2037)
• Store Compression: Term Vector Vector (#2049)

Enhancements:

• Return 503 when threadpool limit is reached (#2048)
• Allow to pass es.default. settings to the process, using it as default value unless specified in the config file (#2016)
• Allow to filter client and “just” data nodes from controlling elected master (default client to true) (#2014)
• Upgrade to Netty 3.5.0.Final (#2013)
• Init script in Debian package ignores some options in elasticsearch.yml (#1765)
• Index level allocation filtering: Add _host option (#1991)
• Multi Search API: Allow to set search_type on REST endpoint URI to apply to all search requests (#2023)
• Query DSL:
  • Add more fuzzy options in different queries (text, query_string/field) (#1974)
  • Add max_boost to custom_filters_score to cap boosting (#1973)
  • term/terms filter performance improvement (bulk reading) (#1972)
  • text query to support minimum_should_match (#1971)
  • Add null_value and existence to missing filter, filtering both null values and missing fields (#1970)
• Rest API: Add HEAD support for /{index}/{type}/{id} to quickly check if doc exists or not (#2047)

Bug fixes:

• Failure to recover properly on node(s) restart (#2046)
• Improve cluster resiliency to disconnected sub clusters + fix a shard allocation bug with quick rolling restarts (#2042)
• fix bug index.ttl.disable_purge should be in IndexMetaData (#2020)
• .DS_Store file in .deb package (#2017)
• Quoted query_string gives NullPointerException with not_analyzed field (0.19.4) (#2006)
• TransportClient does not load plugins (#1982)
• Get mapping with no index specified on an empty cluster returns 404 (#1976)
• River name re-use not possible between node shutdowns (#1921)