How to Change settings and mappings on existing index in Elasticsearch

In Elasticsearch, changing the settings and mappings of existing indices primarily involves the following steps:

1. Close the Index

Before modifying index settings, you must close the index because most settings cannot be altered while it is open. Use the following API to close the index:

bash
POST /your_index/_close

2. Update Index Settings

Once the index is closed, you can modify settings that are otherwise unchangeable while the index is active. Use the following API to update index settings:

bash
PUT /your_index/_settings
{
  "settings": {
    "index": {
      "number_of_replicas": 2,
      "refresh_interval": "30s"
    }
  }
}

In this example, I updated the number of replicas and the index refresh interval.

3. Open the Index

After applying the settings changes, reopen the index to activate the modifications:

bash
POST /your_index/_open

4. Update Mappings

Updating mappings can be more complex, as not all changes are permitted. For instance, you cannot alter the data type of an existing field. However, you can add new fields or modify search-related settings for existing fields. Here is an example of adding a new field:

bash
PUT /your_index/_mapping
{
  "properties": {
    "new_field": {
      "type": "text"
    }
  }
}

Here, I added a new text field named new_field to the index.

Notes

• Always test and back up your data before performing these operations, especially in production environments.
• Changes to settings and mappings may significantly impact index performance.
• For mappings that cannot be directly modified, consider reindexing to a new index with the required settings and mappings.

By following these steps, you can effectively modify index settings and mappings in Elasticsearch. These operations are essential for maintaining and optimizing index performance.