20_Denormalization.asciidoc

Denormalizing Your Data

The way to get the best search performance out of Elasticsearch is to use it as it is intended, by denormalizing your data at index time. Having redundant copies of data in each document that requires access to it removes the need for joins.

If we want to be able to find a blog post by the name of the user who wrote it, include the user’s name in the blog-post document itself:

PUT /my_index/user/1
{
  "name":     "John Smith",
  "email":    "[email protected]",
  "dob":      "1970/10/24"
}

PUT /my_index/blogpost/2
{
  "title":    "Relationships",
  "body":     "It's complicated...",
  "user":     {
    "id":       1,
    "name":     "John Smith" (1)
  }
}

1. Part of the user’s data has been denormalized into the blogpost document.

Now, we can find blog posts about relationships by users called John with a single query:

GET /my_index/blogpost/_search
{
  "query": {
    "bool": {
      "must": [
        { "match": { "title":     "relationships" }},
        { "match": { "user.name": "John"          }}
      ]
    }
  }
}

The advantage of data denormalization is speed. Because each document contains all of the information that is required to determine whether it matches the query, there is no need for expensive joins.