OpenSearch/docs/reference/ilm/actions/ilm-shrink.asciidoc

[role="xpack"]
[[ilm-shrink]]
=== Shrink

Phases allowed: warm

Sets an index to <<dynamic-index-settings, read-only>> 
and shrinks it into a new index with fewer primary shards. 
The name of the new index is of the form `shrink-<original-index-name>`. 
For example, if the name of the source index is _logs_, 
the name of the shrunken index is _shrink-logs_.

The shrink action allocates all primary shards of the index to one node so it 
can call  the <<indices-shrink-index,Shrink API>> to shrink the index.
After shrinking, it swaps aliases that point to the original index to the new shrunken index. 

[IMPORTANT]
If the shrink action is used on a <<ccr-put-follow,follower index>>, 
policy execution waits until the leader index rolls over (or is
<<skipping-rollover, otherwise marked complete>>), 
then converts the follower index into a regular index with the 
<<ilm-unfollow-action,the Unfollow action>> before performing the shrink operation.

If the managed index is part of a <<data-streams, data stream>>,
the shrunken index replaces the original index in the data stream.

[NOTE]
This action cannot be performed on a data stream's write index. Attempts to do
so will fail. To shrink the index, first
<<manually-roll-over-a-data-stream,manually roll over>> the data stream. This
creates a new write index. Because the index is no longer the stream's write
index, the action can resume shrinking it.
Using a policy that makes use of the <<ilm-rollover, rollover>> action
in the hot phase will avoid this situation and the need for a manual rollover for future
managed indices.

[[ilm-shrink-options]]
==== Shrink options
`number_of_shards`::
(Required, integer) 
Number of shards to shrink to. 
Must be a factor of the number of shards in the source index.


[[ilm-shrink-ex]]
==== Example
 
[source,console]
--------------------------------------------------
PUT _ilm/policy/my_policy
{
  "policy": {
    "phases": {
      "warm": {
        "actions": {
          "shrink" : {
            "number_of_shards": 1
          }
        }
      }
    }
  }
}
--------------------------------------------------