From f8c8a10f05847e6757f74bbaa3fbfed8b45a11b3 Mon Sep 17 00:00:00 2001
From: Lee Hinman <dakrone@users.noreply.github.com>
Date: Wed, 5 Feb 2020 09:37:12 -0700
Subject: [PATCH] Add documentation about ILM forcemerge with best_compression
 (#51893)

This adds the option to the parameter list and a warning about the index being unavailable during
the close and open operations.

Relates to #49974
---
 docs/reference/ilm/policy-definitions.asciidoc | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/docs/reference/ilm/policy-definitions.asciidoc b/docs/reference/ilm/policy-definitions.asciidoc
index 4cfa8748916..0f2c5f531ab 100644
--- a/docs/reference/ilm/policy-definitions.asciidoc
+++ b/docs/reference/ilm/policy-definitions.asciidoc
@@ -300,12 +300,17 @@ most a specific number of <<indices-segments,segments>>.
 [options="header"]
 |======
 | Name                 | Required  | Default             | Description
-| `max_num_segments`   | yes       | -                   | The number of
-                                                           segments to merge to.
-                                                           To fully merge the
-                                                           index, set it to `1`
+| `max_num_segments`   | yes       | -                   | The number of segments to merge to. To fully merge the index, set it to `1`
+| `codec`              | no        | -                   | Optional specification of the `best_compression` codec
 |======
 
+[WARNING]
+======
+When using the `"codec": "best_compression"` configuration in the ILM forcemerge action, ILM will
+<<indices-close,close>> and then <<indices-open-close,re-open>> the index prior to a forcemerge.
+During this time the index will be unavailable for either read or write operations.
+======
+
 [source,console]
 --------------------------------------------------
 PUT _ilm/policy/my_policy