How to Use Routing in Elasticsearch for Efficient Data Access

In Elasticsearch, routing is used to control which shard a document is stored in or searched from by specifying a routing key. You add a routing parameter when indexing or querying documents to improve performance by targeting specific shards instead of all shards.

Syntax

Routing in Elasticsearch is specified using the routing parameter in both indexing and search requests. This parameter determines the shard where the document is stored or searched.

• Indexing: Use routing to assign a document to a shard.
• Searching: Use routing to limit search to a specific shard.

json

POST /my_index/_doc/1?routing=user123
{
  "field": "value"
}

GET /my_index/_search?routing=user123
{
  "query": {
    "match_all": {}
  }
}

Example

This example shows how to index a document with a routing key and then search using the same routing key to query only the shard containing that document.

json

PUT /my_index/_doc/1?routing=user123
{
  "name": "Alice",
  "age": 30
}

GET /my_index/_search?routing=user123
{
  "query": {
    "match": {
      "name": "Alice"
    }
  }
}

Output

{
  "hits": {
    "total": 1,
    "hits": [
      {
        "_id": "1",
        "_source": {
          "name": "Alice",
          "age": 30
        }
      }
    ]
  }
}

Common Pitfalls

Common mistakes when using routing include:

• Not using the same routing key for indexing and searching, causing queries to miss documents.
• Using routing unnecessarily, which can reduce Elasticsearch's ability to balance data across shards.
• Forgetting to specify routing on search requests when documents were indexed with routing, resulting in empty results.

json

/* Wrong: Index with routing but search without routing */
PUT /my_index/_doc/2?routing=user456
{
  "name": "Bob"
}

GET /my_index/_search
{
  "query": {
    "match": {
      "name": "Bob"
    }
  }
}

/* Right: Search with the same routing */
GET /my_index/_search?routing=user456
{
  "query": {
    "match": {
      "name": "Bob"
    }
  }
}

Quick Reference

Operation	Routing Usage	Description
Indexing	Specify routing parameter	Assign document to shard based on routing key
Searching	Specify routing parameter	Limit search to shard with routing key
Update/Delete	Specify routing parameter	Target document shard for update or delete
No Routing	Omit routing	Elasticsearch uses default routing (document ID)

Key Takeaways

Use the same routing key when indexing and searching to ensure correct shard targeting.

Routing improves performance by limiting operations to specific shards.

Avoid unnecessary routing to maintain balanced shard distribution.

Specify routing in update and delete requests if used during indexing.

If routing is not specified, Elasticsearch uses the document ID to route data.