Index Settings

There are many many knobs that you can twiddle to customize index behavior, which you can read about in the Index Modules reference documentation, but…​

Elasticsearch comes with good defaults. Don’t twiddle these knobs until you understand what they do and why you should change them.

Two of the most important settings are as follows:

number_of_shards
The number of primary shards that an index should have, which defaults to 5. This setting cannot be changed after index creation.
number_of_replicas
The number of replica shards (copies) that each primary shard should have, which defaults to 1. This setting can be changed at any time on a live index.

For instance, we could create a small index—​just one primary shard—​and no replica shards with the following request:

PUT /my_temp_index
{
    "settings": {
        "number_of_shards" :   1,
        "number_of_replicas" : 0
    }
}

Later, we can change the number of replica shards dynamically using the update-index-settings API as follows:

PUT /my_temp_index/_settings
{
    "number_of_replicas": 1
}