Elasticsearch Index

Elasticsearch Index

Opster Team

July 2020, Version: 1.7-7.9

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Index in Elasticsearch

What it is

In Elasticsearch, an index (indices in plural) can be thought of as a table inside a database that has a schema and can have one or more shards and replicas. An Elasticsearch index is divided into shards and each shard is an instance of a Lucene index.

Indices are used to store the documents in dedicated data structures corresponding to the data type of fields. For example, text fields are stored inside an inverted index whereas numeric and geo fields are stored inside BKD trees.

Create Index

The following example is based on Elasticsearch version 5.x onwards. An index with two shards, each having one replica will be created with the name test_index1

PUT /test_index1?pretty
    "settings" : {
        "number_of_shards" : 2,
        "number_of_replicas" : 1
    "mappings" : {
        "properties" : {
            "tags" : { "type" : "keyword" },
            "updated_at" : { "type" : "date" }
List Indices

All the index names and their basic information can be retrieved using the following command:

GET _cat/indices?v
Index a document

Let’s add a document in the index with below command:

PUT test_index1/_doc/1
  "tags": [
  "date": "01-01-2020"
Query an index
GET test_index1/_search
  "query": {
    "match_all": {}
Query Multiple Indices

It is possible to search multiple indices with a single request. If it is a raw HTTP request, Index names should be sent in comma-separated format, as shown in the example below, and in the case of a query via a programming language client such as python or Java, index names are to be sent in a list format.

GET test_index1,test_index2/_search
Delete Indices
DELETE test_index1

Common Problems

  • It is good practice to define the settings and mapping of an Index wherever possible because if this is not done, Elasticsearch tries to automatically guess the data type of fields at the time of indexing. This automatic process may have disadvantages, such as mapping conflicts, duplicate data and incorrect data types being set in the index. If the fields are not known in advance, it’s better to use dynamic index templates.
  • Elasticsearch supports wildcard patterns in Index names, which sometimes aids with querying multiple indices, but can also be very destructive too. For example, It is possible to delete all the indices in a single command using the following commands:

To disable this, you can add the following lines in the elasticsearch.yml:

action.destructive_requires_name: true

Related log errors to this ES concept

Top warming has been interrupted
Starting segment upgrade upgradeOnlyAncientSegments=
Adding index
Adding index ; preferred over
Dropping index due to conflict with
Removing index
Failed to acquire searcher; source
found shard on path: with a different index UUID this
failed to obtain shard lock
Failed to notify index event listener
Timed out waiting for relocation hand-off to complete
Failed to perform engine refresh

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