OpenSearch/docs/reference/indices/shrink-index.asciidoc

[[indices-shrink-index]]
=== Shrink index API
++++
<titleabbrev>Shrink index</titleabbrev>
++++

Shrinks an existing index into a new index with fewer primary shards.


[source,console]
----
POST /twitter/_shrink/shrunk-twitter-index
----
// TEST[s/^/PUT twitter\n{"settings":{"index.number_of_shards":2,"blocks.write":true}}\n/]


[[shrink-index-api-request]]
==== {api-request-title}

`POST /<index>/_shrink/<target-index>`

`PUT /<index>/_shrink/<target-index>`


[[shrink-index-api-prereqs]]
==== {api-prereq-title}

Before you can shrink an index:

* The index must be read-only.
* A copy of every shard in the index must reside on the same node.
* The <<cluster-health, cluster health>> status must be green.

These three conditions can be achieved with the following request:

[source,console]
--------------------------------------------------
PUT /my_source_index/_settings
{
  "settings": {
    "index.routing.allocation.require._name": "shrink_node_name", <1>
    "index.blocks.write": true <2>
  }
}
--------------------------------------------------
// TEST[s/^/PUT my_source_index\n{"settings":{"index.number_of_shards":2}}\n/]

<1> Forces the relocation of a copy of each shard to the node with name
    `shrink_node_name`.  See <<shard-allocation-filtering>> for more options.

<2> Prevents write operations to this index while still allowing metadata
    changes like deleting the index.

It can take a while to relocate the source index.  Progress can be tracked
with the <<cat-recovery,`_cat recovery` API>>, or the <<cluster-health,
`cluster health` API>> can be used to wait until all shards have relocated
with the `wait_for_no_relocating_shards` parameter.


[[shrink-index-api-desc]]
==== {api-description-title}

The shrink index API allows you to shrink an existing index into a new index
with fewer primary shards. The requested number of primary shards in the target index
must be a factor of the number of shards in the source index. For example an index with
`8` primary shards can be shrunk into `4`, `2` or `1` primary shards or an index
with `15` primary shards can be shrunk into `5`, `3` or `1`. If the number
of shards in the index is a prime number it can only be shrunk into a single
primary shard. Before shrinking, a (primary or replica) copy of every shard
in the index must be present on the same node.

[[how-shrink-works]]
===== How shrinking works

A shrink operation:

. Creates a new target index with the same definition as the source
  index, but with a smaller number of primary shards.

. Hard-links segments from the source index into the target index. (If
  the file system doesn't support hard-linking, then all segments are copied
  into the new index, which is a much more time consuming process. Also if using 
  multiple data paths, shards on different data paths require a full copy of 
  segment files if they are not on the same disk since hardlinks don’t work across
  disks)

. Recovers the target index as though it were a closed index which
  had just been re-opened.


[[_shrinking_an_index]]
===== Shrink an index

To shrink `my_source_index` into a new index called `my_target_index`, issue
the following request:

[source,console]
--------------------------------------------------
POST /my_source_index/_shrink/my_target_index
{
  "settings": {
    "index.routing.allocation.require._name": null, <1>
    "index.blocks.write": null <2>
  }
}
--------------------------------------------------
// TEST[continued]

<1> Clear the allocation requirement copied from the source index.
<2> Clear the index write block copied from the source index.

The above request returns immediately once the target index has been added to
the cluster state -- it doesn't wait for the shrink operation to start.

[IMPORTANT]
=====================================

Indices can only be shrunk if they satisfy the following requirements:

* the target index must not exist

* The index must have more primary shards than the target index.

* The number of primary shards in the target index must be a factor of the
  number of primary shards in the source index. The source index must have
  more primary shards than the target index.

* The index must not contain more than `2,147,483,519` documents in total
  across all shards that will be shrunk into a single shard on the target index
  as this is the maximum number of docs that can fit into a single shard.

* The node handling the shrink process must have sufficient free disk space to
  accommodate a second copy of the existing index.

=====================================

The `_shrink` API is similar to the <<indices-create-index, `create index` API>>
and accepts `settings` and `aliases` parameters for the target index:

[source,console]
--------------------------------------------------
POST /my_source_index/_shrink/my_target_index
{
  "settings": {
    "index.number_of_replicas": 1,
    "index.number_of_shards": 1, <1>
    "index.codec": "best_compression" <2>
  },
  "aliases": {
    "my_search_indices": {}
  }
}
--------------------------------------------------
// TEST[s/^/PUT my_source_index\n{"settings": {"index.number_of_shards":5,"index.blocks.write": true}}\n/]

<1> The number of shards in the target index. This must be a factor of the
    number of shards in the source index.
<2> Best compression will only take affect when new writes are made to the
    index, such as when <<indices-forcemerge,force-merging>> the shard to a single
    segment.


NOTE: Mappings may not be specified in the `_shrink` request.


[[monitor-shrink]]
===== Monitor the shrink process

The shrink process can be monitored with the <<cat-recovery,`_cat recovery`
API>>, or the <<cluster-health, `cluster health` API>> can be used to wait
until all primary shards have been allocated by setting the  `wait_for_status`
parameter to `yellow`.

The `_shrink` API returns as soon as the target index has been added to the
cluster state, before any shards have been allocated. At this point, all
shards are in the state `unassigned`. If, for any reason, the target index
can't be allocated on the shrink node, its primary shard will remain
`unassigned` until it can be allocated on that node.

Once the primary shard is allocated, it moves to state `initializing`, and the
shrink process begins. When the shrink operation completes, the shard will
become `active`. At that  point, Elasticsearch will try to allocate any
replicas and may decide to relocate the primary shard to another node.


[[shrink-wait-active-shards]]
===== Wait for active shards

Because the shrink operation creates a new index to shrink the shards to,
the <<create-index-wait-for-active-shards,wait for active shards>> setting
on index creation applies to the shrink index action as well.


[[shrink-index-api-path-params]]
==== {api-path-parms-title}

`<index>`::
(Required, string)
Name of the source index to shrink.

include::{docdir}/rest-api/common-parms.asciidoc[tag=target-index]

[[shrink-index-api-query-params]]
==== {api-query-parms-title}

include::{docdir}/rest-api/common-parms.asciidoc[tag=wait_for_active_shards]

include::{docdir}/rest-api/common-parms.asciidoc[tag=timeoutparms]


[[shrink-index-api-request-body]]
==== {api-request-body-title}

include::{docdir}/rest-api/common-parms.asciidoc[tag=target-index-aliases]

include::{docdir}/rest-api/common-parms.asciidoc[tag=target-index-settings]