Chapter 1: Understanding Reindexing in Elasticsearch

In this article, we delve into a vital function within Elasticsearch: the process of reindexing. Reindexing allows users to replicate existing data from a source index to a destination index. This can occur between different clusters or within the same cluster, essentially transferring data from one index to another.

Does Elasticsearch provide an API for reindexing?

The answer is a resounding yes! Elasticsearch has designed a specific API endpoint that simplifies this process for you. This endpoint is referred to as _reindex.

To utilize this API, you need to execute a POST HTTP request like this:

POST _reindex

{

"source": {

"index": "{{source-index-name}}"

},

"dest": {

"index": "{{dest-index-name}}"

}

}

Ensure you replace the placeholders {{source-index-name}} and {{dest-index-name}} with your actual index names. It’s important to note that both indexes must already exist prior to making this API call; the _reindex operation will not create either index automatically.

Section 1.1: Reasons for Reindexing

There are several reasons one might consider reindexing. For example, you may need to accommodate changes in data types, introduce new fields that require population, or update mappings due to modifications in existing fields.

Section 1.2: Important Considerations

One critical point to remember is that the _reindex API does not automatically transfer any settings from the source index to the destination index. Additionally, you have the option to execute the Reindex API call asynchronously.

To enable this, you can include the query parameter wait_for_completion=false in your request:

POST _reindex?wait_for_completion=false

In this scenario, Elasticsearch performs preliminary checks, initiates the request, and returns a task ID that you can use to monitor the progress or cancel the request if needed. This is different from the default behavior where the request will block until the entire reindexing process is finished, which can be time-consuming.

Chapter 2: Video Tutorials

For a more detailed understanding of reindexing in Elasticsearch, check out the following video resources.

In this tutorial, learn how to utilize the Elasticsearch Reindex API from Kibana, including how to change the mapping of an index.

Discover how to change the mapping in an index using Elasticsearch, with step-by-step instructions on the process.