[[cluster-update-settings]]
== Cluster Update Settings

Use this API to review and change cluster-wide settings. 

To review cluster settings:

[source,js]
--------------------------------------------------
GET /_cluster/settings
--------------------------------------------------
// CONSOLE

Updates to settings can be persistent, meaning they apply across restarts, or transient, where they don't 
survive a full cluster restart. Here is an example of a persistent update:

[source,js]
--------------------------------------------------
PUT /_cluster/settings
{
    "persistent" : {
        "indices.recovery.max_bytes_per_sec" : "50mb"
    }
}
--------------------------------------------------
// CONSOLE

This update is transient:

[source,js]
--------------------------------------------------
PUT /_cluster/settings?flat_settings=true
{
    "transient" : {
        "indices.recovery.max_bytes_per_sec" : "20mb"
    }
}
--------------------------------------------------
// CONSOLE

The response to an update returns the changed setting, as in this response to the transient example:

[source,js]
--------------------------------------------------
{
    ...
    "persistent" : { },
    "transient" : {
        "indices.recovery.max_bytes_per_sec" : "20mb"
    }
}
--------------------------------------------------
// TESTRESPONSE[s/\.\.\./"acknowledged": true,/]

You can reset persistent or transient settings by assigning a
`null` value. If a transient setting is reset, the first one of these values that is defined is applied:

* the persistent setting
* the setting in the configuration file
* the default value. 

This example resets a setting:

[source,js]
--------------------------------------------------
PUT /_cluster/settings
{
    "transient" : {
        "indices.recovery.max_bytes_per_sec" : null
    }
}
--------------------------------------------------
// CONSOLE

The response does not include settings that have been reset:

[source,js]
--------------------------------------------------
{
    ...
    "persistent" : {},
    "transient" : {}
}
--------------------------------------------------
// TESTRESPONSE[s/\.\.\./"acknowledged": true,/]

You can also reset settings using wildcards. For example, to reset
all dynamic `indices.recovery` settings:

[source,js]
--------------------------------------------------
PUT /_cluster/settings
{
    "transient" : {
        "indices.recovery.*" : null
    }
}
--------------------------------------------------
// CONSOLE


[float]
=== Order of Precedence

The order of precedence for cluster settings is:

1. transient cluster settings 
2. persistent cluster settings
3. settings in the `elasticsearch.yml` configuration file.

It's best to use the `elasticsearch.yml` file only
for local configurations, and set all cluster-wide settings with the
`settings` API.

You can find the list of settings that you can dynamically update in <<modules,Modules>>.

