Reindexing data in Elasticsearch

Introduction

Reindexing data helps you copy or move data from one place to another inside Elasticsearch. It is useful when you want to change the structure or fix mistakes without losing data.

You want to change the mapping or settings of an index.

You need to move data from an old index to a new one with a different name.

You want to filter or modify documents while copying them.

You want to upgrade Elasticsearch and reorganize your data.

You want to fix corrupted or incomplete data by copying only good documents.

Syntax

Elasticsearch

POST _reindex
{
  "source": {
    "index": "old_index"
  },
  "dest": {
    "index": "new_index"
  }
}

The source section tells Elasticsearch where to copy data from.

The dest section tells where to copy data to.

Examples

Copies all documents from products_v1 to products_v2.

Elasticsearch

POST _reindex
{
  "source": { "index": "products_v1" },
  "dest": { "index": "products_v2" }
}

Copies only documents with status equal to error from logs to error_logs.

Elasticsearch

POST _reindex
{
  "source": {
    "index": "logs",
    "query": { "term": { "status": "error" } }
  },
  "dest": { "index": "error_logs" }
}

Adds a new field with a default value to each document while copying.

Elasticsearch

POST _reindex
{
  "source": { "index": "old_index" },
  "dest": { "index": "new_index" },
  "script": {
    "source": "ctx._source['new_field'] = 'default_value'"
  }
}

Sample Program

This command copies all documents from the library_books index to a new index called library_books_backup. It is like making a backup copy of your data.

Elasticsearch

POST _reindex
{
  "source": {
    "index": "library_books"
  },
  "dest": {
    "index": "library_books_backup"
  }
}

Important Notes

Reindexing can take time depending on how much data you have.

You can use a query to copy only some documents.

Use script to change data while copying.

Summary

Reindexing copies data from one index to another.

It helps change data structure or fix issues without losing data.

You can filter or modify data during reindexing.