What is _id in Elasticsearch: Explanation and Usage

In Elasticsearch, _id is a unique identifier for each document within an index. It acts like a name tag that helps Elasticsearch find, update, or delete a specific document quickly.

How It Works

Think of _id as a unique name tag for every document stored in Elasticsearch. Just like your ID card helps others recognize you among many people, _id helps Elasticsearch find one document among millions.

When you add a document, Elasticsearch either lets you set your own _id or creates one automatically. This ID is then used internally to quickly locate, update, or remove that document without scanning the whole index.

This system makes Elasticsearch very fast because it doesn’t have to search through all documents; it just looks for the unique _id you provide or it generated.

Example

This example shows how to add a document with a custom _id and then retrieve it using that _id.

json

PUT /my_index/_doc/123
{
  "name": "Alice",
  "age": 30
}

GET /my_index/_doc/123

Output

{
  "_index": "my_index",
  "_id": "123",
  "_version": 1,
  "found": true,
  "_source": {
    "name": "Alice",
    "age": 30
  }
}

When to Use

Use _id whenever you need to uniquely identify a document in Elasticsearch. This is important for updating or deleting specific documents without confusion.

For example, if you store user profiles, you might use the user’s unique ID as the _id. This way, you can quickly update a user’s information or fetch their profile by referencing their _id.

Also, if you don’t provide an _id, Elasticsearch will create one for you, which is fine for many cases where you don’t need to control the ID yourself.

Key Points

• _id uniquely identifies each document in an Elasticsearch index.
• You can set your own _id or let Elasticsearch generate one automatically.
• _id helps Elasticsearch quickly find, update, or delete documents.
• Using meaningful _id values can simplify document management in your application.

Key Takeaways

_id is the unique identifier for documents in Elasticsearch.

You can assign your own _id or let Elasticsearch generate it automatically.

_id enables fast access to documents for retrieval, updates, or deletion.

Using custom _id values helps manage documents more clearly in your app.