No special upgrade steps are needed from 0.16.1.

Breaking changes:

• Field Cache: Change default type to resident from soft (#958)
• Filter Cache: Introduce new node level filter cache and make it default (#959)

Enhancements:

• Upgrade to jackson 1.8.1 (#941)
• Analysis:
  • Pattern Tokenizer (#928)
  • Add elision token filter (#930)
  • Phonetic filter to support cologne encoder (#942)
• Field Cache: Allow to set index.cache.field.expire when using resident type (#957)
• Query DSL:
  • query_string – Expose QueryParser#setAutoGeneratePhraseQueries (#964)
  • Ids Filter / Query – allow to execute it with no type defined / several types (#969)
  • Add limit filter (#976)
• Scripting: Optimize to native script execution when using just doc.score (#952)

Bug fixes:

• Deleting and recreating a new index with dynamic mapping can cause type failures (#931)
• wrong type returned by date_histogram (#932)
• IBM J9 failure to serialize nodes info (#950)
• NPE when using “not” filter (#953)
• Analysis: Regression (0.16.1), Camel cased filters / tokenizers failed to load in custom analyzer (#937)
• Filter Cache: soft filter cache can cause bad memory behavior (#946)
• Mapping: dynamic templates of object type do not initialize some mapping data structures (like analyzers lookup) (#929)
• Mapping – Date Format: 3 or more custom date formats fail using ‘||’ delimiter (#977)
• Scripting – mvel: Fix thread safety misuse when compiling scripts (#886)
• Search: Empty facets element causes search failures (#938)
• auto_expand_replicas: [0-all] can cause data loss when nodes are removed (#934)