Upgrade Notes:

• Upgrading from 0.19 requires a full cluster restart.

Breaking changes:

• Deprecate Experimental Snappy Support (#2459)
• Deprecate Shared Gateway (#2458)
• Mapping: string mapping to automatically set omit_norms to true and index_options to docs when setting index to not_analyzed (#2349)
• Shard Allocation: add index.routing.allocation.require…. and cluster.routing.allocation.require…. setting (#2404)

New features:

• Indexing Slow Log (#2457)

Enhancements:

• Expose ES version in node info api (#2466)
• Expose fragmenter option for plain highlighter (#2465)
• Upgrade to Netty 3.5.11 (#2456)
• Add types and stats to search slow log (#2455)
• Cannot change MatchQuery behaviour with 0 terms (#2429)
• Upgrade to netty 3.5.10 (#2399)
• Upgrade to Netty 3.5.9 (#2377)
• Upsert doesn’t return fields (#2362)
• Node Stats: Add largest thread pool count per thread pool stats (#2382)

Bug fixes:

• Wildcard query on non existent field matches all documents. (#2461) 
• The relevancy score in explanation of custom_filters_query doesn’t match the actual score (#2441)
• Match query should fail when trying to provide several fields in its simplified form (#2432)
• Setting logger levels using cluster update settings does not work (#2428)
• NullPointerException with prefix query (#2408)
• Deriving the REST status code from a failure can, very rarely, cause an infinite loop (#2402)
• Adding a type with _source or _all enabled fails, when these are disabled in index (#2394)
• Ignore indices not set when using multi search api. (#2380)
• path_match support in dynamic templates is incorrect (#2371)
• Deleting a non-existent warmer causes ES to hang (#2363)
• MapperParsingException on percolation with _size enabled (#2352)
• Multi Match: tie_breaker should allow for floating point value (#2397)
• 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)