[[snapshots-restore-snapshot]]
== Restore indices from a snapshot

++++
<titleabbrev>Restore a snapshot</titleabbrev>
++++

////
[source,console]
-----------------------------------
PUT /_snapshot/my_backup
{
  "type": "fs",
  "settings": {
    "location": "my_backup_location"
  }
}

PUT /_snapshot/my_backup/snapshot_1?wait_for_completion=true
-----------------------------------
// TESTSETUP

////

A snapshot can be restored using the following command:

[source,console]
-----------------------------------
POST /_snapshot/my_backup/snapshot_1/_restore
-----------------------------------

By default, all indices in the snapshot are restored, and the cluster state is
*not* restored. It's possible to select indices that should be restored as well
as to allow the global cluster state from being restored by using `indices` and
`include_global_state` options in the restore request body. The list of indices
supports <<multi-index,multi index syntax>>. The `rename_pattern`
and `rename_replacement` options can be also used to rename indices on restore
using regular expression that supports referencing the original text as
explained
http://docs.oracle.com/javase/6/docs/api/java/util/regex/Matcher.html#appendReplacement(java.lang.StringBuffer,%20java.lang.String)[here].
Set `include_aliases` to `false` to prevent aliases from being restored together
with associated indices.

[source,console]
-----------------------------------
POST /_snapshot/my_backup/snapshot_1/_restore
{
  "indices": "index_1,index_2",
  "include_aliases": false,
  "ignore_unavailable": true,
  "include_global_state": true,
  "rename_pattern": "index_(.+)",
  "rename_replacement": "restored_index_$1"
}
-----------------------------------
// TEST[continued]

The restore operation can be performed on a functioning cluster. However, an
existing index can be only restored if it's <<indices-open-close,closed>> and
has the same number of shards as the index in the snapshot. The restore
operation automatically opens restored indices if they were closed and creates
new indices if they didn't exist in the cluster. If cluster state is restored
with `include_global_state` (defaults to `false`), the restored templates that
don't currently exist in the cluster are added and existing templates with the
same name are replaced by the restored templates. The restored persistent
settings are added to the existing persistent settings.

[float]
=== Partial restore

By default, the entire restore operation will fail if one or more indices participating in the operation don't have
snapshots of all shards available. It can occur if some shards failed to snapshot for example. It is still possible to
restore such indices by setting `partial` to `true`. Please note, that only successfully snapshotted shards will be
restored in this case and all missing shards will be recreated empty.


[float]
=== Changing index settings during restore

Most of index settings can be overridden during the restore process. For example, the following command will restore
the index `index_1` without creating any replicas while switching back to default refresh interval:

[source,console]
-----------------------------------
POST /_snapshot/my_backup/snapshot_1/_restore
{
  "indices": "index_1",
  "ignore_unavailable": true,
  "index_settings": {
    "index.number_of_replicas": 0
  },
  "ignore_index_settings": [
    "index.refresh_interval"
  ]
}
-----------------------------------
// TEST[continued]

Please note, that some settings such as `index.number_of_shards` cannot be changed during restore operation.

[float]
=== Restoring to a different cluster

The information stored in a snapshot is not tied to a particular cluster or a cluster name. Therefore it's possible to
restore a snapshot made from one cluster into another cluster. All that is required is registering the repository
containing the snapshot in the new cluster and starting the restore process. The new cluster doesn't have to have the
same size or topology.  However, the version of the new cluster should be the same or newer (only 1 major version newer) than the cluster that was used to create the snapshot.  For example, you can restore a 1.x snapshot to a 2.x cluster, but not a 1.x snapshot to a 5.x cluster.

If the new cluster has a smaller size additional considerations should be made. First of all it's necessary to make sure
that new cluster have enough capacity to store all indices in the snapshot. It's possible to change indices settings
during restore to reduce the number of replicas, which can help with restoring snapshots into smaller cluster. It's also
possible to select only subset of the indices using the `indices` parameter.

If indices in the original cluster were assigned to particular nodes using
<<shard-allocation-filtering,shard allocation filtering>>, the same rules will be enforced in the new cluster. Therefore
if the new cluster doesn't contain nodes with appropriate attributes that a restored index can be allocated on, such
index will not be successfully restored unless these index allocation settings are changed during restore operation.

The restore operation also checks that restored persistent settings are compatible with the current cluster to avoid accidentally
restoring incompatible settings. If you need to restore a snapshot with incompatible persistent settings, try restoring it without
the global cluster state.

[float]
=== Snapshot status

A list of currently running snapshots with their detailed status information can be obtained using the following command:

[source,console]
-----------------------------------
GET /_snapshot/_status
-----------------------------------
// TEST[continued]

In this format, the command will return information about all currently running snapshots. By specifying a repository name, it's possible
to limit the results to a particular repository:

[source,console]
-----------------------------------
GET /_snapshot/my_backup/_status
-----------------------------------
// TEST[continued]

If both repository name and snapshot id are specified, this command will return detailed status information for the given snapshot even
if it's not currently running:

[source,console]
-----------------------------------
GET /_snapshot/my_backup/snapshot_1/_status
-----------------------------------
// TEST[continued]

The output looks similar to the following:

[source,console-result]
--------------------------------------------------
{
  "snapshots": [
    {
      "snapshot": "snapshot_1",
      "repository": "my_backup",
      "uuid": "XuBo4l4ISYiVg0nYUen9zg",
      "state": "SUCCESS",
      "include_global_state": true,
      "shards_stats": {
        "initializing": 0,
        "started": 0,
        "finalizing": 0,
        "done": 5,
        "failed": 0,
        "total": 5
      },
      "stats": {
        "incremental": {
          "file_count": 8,
          "size_in_bytes": 4704
        },
        "processed": {
          "file_count": 7,
          "size_in_bytes": 4254
        },
        "total": {
          "file_count": 8,
          "size_in_bytes": 4704
        },
        "start_time_in_millis": 1526280280355,
        "time_in_millis": 358
      }
    }
  ]
}
--------------------------------------------------
// TESTRESPONSE[skip: No snapshot status to validate.]

The output is composed of different sections. The `stats` sub-object provides details on the number and size of files that were
snapshotted. As snapshots are incremental, copying only the Lucene segments that are not already in the repository,
the `stats` object contains a `total` section for all the files that are referenced by the snapshot, as well as an `incremental` section
for those files that actually needed to be copied over as part of the incremental snapshotting. In case of a snapshot that's still
in progress, there's also a `processed` section that contains information about the files that are in the process of being copied.

Multiple ids are also supported:

[source,console]
-----------------------------------
GET /_snapshot/my_backup/snapshot_1,snapshot_2/_status
-----------------------------------
// TEST[skip: no snapshot_2 to get]
