Update slice parameter with additional information (#3350) (#3398)

* Update slice parameter with additional information



* Update _api-reference/document-apis/reindex.md

* doc review updates



---------


(cherry picked from commit 46a3426)

Signed-off-by: ariamarble <[email protected]>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

_api-reference/document-apis/reindex.md

@@ -1,15 +1,15 @@
 ---
 layout: default
-title: Reindex
+title: Reindex document
 parent: Document APIs
 nav_order: 60
 ---
 
-# Index document
+# Reindex document
 Introduced 1.0
 {: .label .label-purple}
 
-The reindex API operation lets you copy all or a subset of your data from a source index into a destination index.
+The reindex document API operation lets you copy all or a subset of your data from a source index into a destination index.
 
 ## Example
 
@@ -66,7 +66,7 @@ password | Password to authenticate with the remote cluster.
 socket_timeout | The wait time for socket reads. Default is 30s.
 connect_timeout | The wait time for remote connection timeouts. Default is 30s.
 size | The number of documents to reindex.
-slice | Whether to manually or automatically slice the reindex operation so it executes in parallel.
+slice | Whether to manually or automatically slice the reindex operation so it executes in parallel. Setting this field to `auto` allows OpenSearch to control the number of slices to use, which is one slice per shard, up to a maximum of 20. If there are multiple sources, the number of slices used are based on the index or backing index with the smallest number of shards.
 _source | Whether to reindex source fields. Specify a list of fields to reindex or true to reindex all fields. Default is true.
 id | The ID to associate with manual slicing.
 max | Maximum number of slices.