ElasticSearch is a distributed search engine that is a wrapper around Lucene. It stores data in segments which are mini-indexes that are immutable, with new segments regularly added and old segments merged. It maintains warm caches for old segments containing most data and cold caches for new segments.

1. ElasticSearch

2. What is ElasticSearch?
• Distributed Search Engine
• Lucene wrapper

8. Segments (mini-index)
• Segments are immutable (doc del is marked as del and
later cleaned up).
• New segments are added at regular intervals. Segments
are merged.
• Warm caches for old segments which have majority of
data.
• Cold caches for new segments.

11. –Franklin D. Roosevelt
“A smooth sea never made a skilful sailor.”