Elasticsearch.org All About Elasticsearch Filter BitSets | Blog | Elasticsearch

Elasticsearch.org All About Elasticsearch Filter BitSets | Blog | Elasticsearch

When building queries in Elasticsearch, you'll often find yourself composing sets of filters. Say you need to filter users that are: Gender: Male Age: 23-26 Language: English Generally you should place these filters inside of a  Boolean Filter . But wait…isn't there an  And Filter ? What about the  Or Filter  and  Not Filters ?  Are they simply an alternative syntax to the Bool filter? The short answer is: No, they are very distinct. More importantly, they can have a big impact on your query performance. BitSets The key to understanding the difference will require a detour into BitSets.  Fundamentally, a  BitSet  is just an array of bits that represent state.  A position in the bit array is either a 1 or a 0. Filters don't score documents – they simply include or exclude.  If a document matches a filter, it is represented with a one in the BitSet; otherwise a zero. This means that Elasticsearch can store an entire segment's filter state ("who matches this particular filter?

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