[[docs-refresh]]
== `?refresh`

The <<docs-index_,Index>>, <<docs-update,Update>>, <<docs-delete,Delete>>, and
<<docs-bulk,Bulk>> APIs support setting `refresh` to control when changes made
by this request are made visible to search. These are the allowed values:

Empty string or `true`::

Refresh the relevant primary and replica shards (not the whole index)
immediately after the operation occurs, so that the updated document appears
in search results immediately. This should *ONLY* be done after careful thought
and verification that it does not lead to poor performance, both from an
indexing and a search standpoint.

`wait_for`::

Wait for the changes made by the request to be made visible by a refresh before
replying. This doesn't force an immediate refresh, rather, it waits for a
refresh to happen. Elasticsearch automatically refreshes shards that have changed
every `index.refresh_interval` which defaults to one second. That setting is
<<dynamic-index-settings,dynamic>>. Calling the <<indices-refresh>> API or
setting `refresh` to `true` on any of the APIs that support it will also
cause a refresh, in turn causing already running requests with `refresh=wait_for`
to return.

`false` (the default)::

Take no refresh related actions. The changes made by this request will be made
visible at some point after the request returns.

[float]
=== Choosing which setting to use

Unless you have a good reason to wait for the change to become visible always
use `refresh=false`, or, because that is the default, just leave the `refresh`
parameter out of the URL. That is the simplest and fastest choice.

If you absolutely must have the changes made by a request visible synchronously
with the request then you must pick between putting more load on
Elasticsearch (`true`) and waiting longer for the response (`wait_for`). Here
are a few points that should inform that decision:

* The more changes being made to the index the more work `wait_for` saves
compared to `true`. In the case that the index is only changed once every
`index.refresh_interval` then it saves no work.
* `true` creates less efficient indexes constructs (tiny segments) that must
later be merged into more efficient index constructs (larger segments). Meaning
that the cost of `true` is payed at index time to create the tiny segment, at
search time to search the tiny segment, and at merge time to make the larger
segments.
* Never start multiple `refresh=wait_for` requests in a row. Instead batch them
into a single bulk request with `refresh=wait_for` and Elasticsearch will start
them all in parallel and return only when they have all finished.
* If the refresh interval is set to `-1`, disabling the automatic refreshes,
then requests with `refresh=wait_for` will wait indefinitely until some action
causes a refresh. Conversely, setting `index.refresh_interval` to something
shorter than the default like `200ms` will make `refresh=wait_for` come back
faster, but it'll still generate inefficient segments.
* `refresh=wait_for` only affects the request that it is on, but, by forcing a
refresh immediately, `refresh=true` will affect other ongoing request. In
general, if you have a running system you don't wish to disturb then
`refresh=wait_for` is a smaller modification.

[float]
=== `refresh=wait_for` Can Force a Refresh

If a `refresh=wait_for` request comes in when there are already
`index.max_refresh_listeners` (defaults to 1000) requests waiting for a refresh
on that shard then that request will behave just as though it had `refresh` set
to `true` instead: it will force a refresh. This keeps the promise that when a
`refresh=wait_for` request returns that its changes are visible for search
while preventing unchecked resource usage for blocked requests. If a request
forced a refresh because it ran out of listener slots then its response will
contain `"forced_refresh": true`.

Bulk requests only take up one slot on each shard that they touch no matter how
many times they modify the shard.

[float]
=== Examples

These will create a document and immediately refresh the index so it is visible:

[source,js]
--------------------------------------------------
PUT /test/test/1?refresh
{"test": "test"}
PUT /test/test/2?refresh=true
{"test": "test"}
--------------------------------------------------
// CONSOLE

These will create a document without doing anything to make it visible for
search:

[source,js]
--------------------------------------------------
PUT /test/test/3
{"test": "test"}
PUT /test/test/4?refresh=false
{"test": "test"}
--------------------------------------------------
// CONSOLE

This will create a document and wait for it to become visible for search:

[source,js]
--------------------------------------------------
PUT /test/test/4?refresh=wait_for
{"test": "test"}
--------------------------------------------------
// CONSOLE
