Enhancements:

• Stop Token Filter – allow to set enable_position_increments (#1182)
• warn if mlockall is not working once enabled in settings (instead of debug logging) (#1194)
• Allow creation of empty docs (#1195)
• Analysis:
  • Unique token filter (#1185)
  • ‘truncate’ token filter (#1165)
  • Add a kstem name option to stemmer token filter (on top of the default kstem option) (#1196)
• Cache Stats: Computing the filter stats using the default weighted filter cache is expensive (#1201)
• Groovy Plugins: Upgrade to 1.8.1 (#1175)
• HTTP: Disable automatic cookie parsing and resetting, allow to enable it (#1177)
• Http Transport: Allow to configure max_header_size, max_initial_line_length, and max_chunk_size (#1174)
• Index Cache Stats / JVM Stats: Add a refresh_interval to control when it gets refreshed (#1200)
• Mapping:
  • Root object non ISO date formats to support timezone (#1181)
  • Renamed root object date_formats to dynamic_date_formats (old value still works) (#1183)
• More Like This API: Allow to provide search_size and search_from (#1179)
• Queries: Optimize single clause boolean query (#1206)
• Query DSL:
  • Allow to control how all multi term queries are rewritten (#1186)
  • ids filter/parse to automatically use types provided as part of the search (#1188)
  • custom_filters_score allow to associate boost on filter instead of script (#1204)
  • custom_filters_score – add score_mode to control filters matching scoring (#1205)
• Rest API: Add an X-Opaque-Id header, to be returned in the response if exists in the request (#1202)
• Search API: URI request allow to additional query_string parameters (#1178)

Bug fixes:

• When flushing, old transaction log is not removed (#1180). Note, this feature has not been properly backported, and will be properly fixed in 0.17.5.
• Failed to load uid from the index in match_all query with parent/child and _source disabled (#1149)
• Merge Policy type setting fails (#1190)
• Sorting on _score in the URI format / Java API is reversed (#1191)
• highlight.fields should accept field names with the full path (#1192)
• Delete By Query wrongly persisted to translog (#1198)
• Automatic index creation can still cause “index missing” failures (#1199)
• Minor(?) scripting bug(?): (caching-related?) odd behavior when changing languages for the same script code (#1150)
• Unicast Discovery: When providing a comma separated list of addresses, trim them from whitespaces (#1193)