Index Management in Elasticsearch

Introduction

Index management in Elasticsearch is crucial for efficient data storage, retrieval, and performance optimization. This tutorial will provide a comprehensive guide on the various aspects of index management, including creation, configuration, monitoring, and maintenance.

Creating an Index

To create an index in Elasticsearch, you can use the PUT request. This request can include various settings and mappings that define the index's structure.

PUT /my_index
{
  "settings": {
    "number_of_shards": 1,
    "number_of_replicas": 0
  },
  "mappings": {
    "properties": {
      "field1": {
        "type": "text"
      }
    }
  }
}

This command creates an index named my_index with one shard and no replicas. It also defines a single field, field1, of type text.

Updating Index Settings

Index settings can be updated dynamically using the PUT request. However, some settings can only be configured at index creation time.

PUT /my_index/_settings
{
  "index": {
    "number_of_replicas": 1
  }
}

This command updates the number of replicas for my_index to 1.

Index Mapping

Mappings define how documents and their fields are stored and indexed. You can add new fields to an existing index, but you cannot change the type of an existing field.

PUT /my_index/_mapping
{
  "properties": {
    "field2": {
      "type": "keyword"
    }
  }
}

This command adds a new field, field2, of type keyword to my_index.

Deleting an Index

To delete an index, use the DELETE request. Note that this operation is irreversible and all data in the index will be lost.

DELETE /my_index

This command deletes the index named my_index.

Monitoring Index Health

Monitoring the health of your indices is crucial for maintaining performance and reliability. Elasticsearch provides various APIs to check the status and statistics of indices.

GET /_cluster/health/my_index

{
  "cluster_name": "elasticsearch",
  "status": "green",
  "timed_out": false,
  "number_of_nodes": 1,
  "number_of_data_nodes": 1,
  "active_primary_shards": 1,
  "active_shards": 1,
  "relocating_shards": 0,
  "initializing_shards": 0,
  "unassigned_shards": 0,
  "delayed_unassigned_shards": 0,
  "number_of_pending_tasks": 0,
  "number_of_in_flight_fetch": 0,
  "task_max_waiting_in_queue_millis": 0,
  "active_shards_percent_as_number": 100.0
}
                

This command retrieves the health status of the index my_index.

Index Aliases

Aliases provide a way to use a single name to refer to one or more indices. This can simplify index management and querying.

POST /_aliases
{
  "actions": [
    {
      "add": {
        "index": "my_index",
        "alias": "my_alias"
      }
    }
  ]
}

This command creates an alias named my_alias for the index my_index.

Reindexing

Reindexing allows you to copy documents from one index to another. This is useful for tasks like changing the index settings or mappings.

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

This command copies all documents from old_index to new_index.

Closing and Opening Indices

Closing an index reduces memory usage by removing its data from memory. You can re-open the index when you need to access it again.

POST /my_index/_close

POST /my_index/_open

The first command closes my_index, and the second one re-opens it.

Index Templates

Index templates allow you to define settings, mappings, and aliases that will be automatically applied to new indices that match a specified pattern.

PUT /_template/my_template
{
  "index_patterns": ["log-*"],
  "settings": {
    "number_of_shards": 1
  },
  "mappings": {
    "properties": {
      "timestamp": {
        "type": "date"
      }
    }
  }
}

This command creates a template named my_template that applies to indices matching the pattern log-*.