What is Elasticsearch Analyzers?

Analyzers are pre-processors which are executed on the Text before generating inverted index. 

So why do we need Analyzers in Elasticsearch?

Consider a field which we want have inverted-index

Document 1: "Hello Elasticsearch World "
Document 2: "hello Elasticsearch world"

The Inverted Index looks like this:

Term	(Document,Frequency)
Hello	(1,1)
World	(1,1)
Elasticsearch	(1,1),(2,1)
hello	(2,1)
world	(2,1)

Its evident that "Hello" and "hello" are same words with change in case, As there are two separate indexes for the same word , the query returns partial result when we need a case insensitive search.

To fix the above issue,Now lets have the words converted to lowercase before creating the inverted-index.

Term	(Document,Frequency)
hello	(1,1),(2,1)
world	(1,1),(2,1)
Elasticsearch	(1,1),(2,1)

This is what analyzers in Elasticsearch are for. This a simple illustration and analyzers are designed to do more than the example used for illustration.

In simple terms an Analyzer does:

1. Split the text into individual terms or token, based on whitespace.
2. Standardize the individual terms so they are searchable.