[[mapping-ttl-field]]
=== `_ttl`

A lot of documents naturally come with an expiration date. Documents can
therefore have a `_ttl` (time to live), which will cause the expired
documents to be deleted automatically.

`_ttl` accepts two parameters which are described below, every other setting will be silently ignored.

[float]
==== enabled

By default it is disabled, in order to enable it, the following mapping
should be defined:

[source,js]
--------------------------------------------------
{
    "tweet" : {
        "_ttl" : { "enabled" : true }
    }
}
--------------------------------------------------

`_ttl` can only be enabled once and never be disabled again.

[float]
==== default

You can provide a per index/type default `_ttl` value as follows:

[source,js]
--------------------------------------------------
{
    "tweet" : {
        "_ttl" : { "enabled" : true, "default" : "1d" }
    }
}
--------------------------------------------------

In this case, if you don't provide a `_ttl` value in your query or in
the `_source` all tweets will have a `_ttl` of one day.

In case you do not specify a time unit like `d` (days), `m` (minutes),
`h` (hours), `ms` (milliseconds) or `w` (weeks), milliseconds is used as
default unit.

If no `default` is set and no `_ttl` value is given then the document
has an infinite `_ttl` and will not expire.

You can dynamically update the `default` value using the put mapping
API. It won't change the `_ttl` of already indexed documents but will be
used for future documents.

[float]
==== Note on documents expiration

Expired documents will be automatically deleted regularly. You can
dynamically set the `indices.ttl.interval` to fit your needs. The
default value is `60s`.

The deletion orders are processed by bulk. You can set
`indices.ttl.bulk_size` to fit your needs. The default value is `10000`.

Note that the expiration procedure handle versioning properly so if a
document is updated between the collection of documents to expire and
the delete order, the document won't be deleted.
