Documentation for scroll size in reindex

docs/reference/docs/reindex.asciidoc

@@ -267,7 +267,7 @@ routing set to `cat`.
 POST /_reindex
 {
   "source": {
-    "index": "source"
+    "index": "source",
     "query": {
       "match": {
         "company": "cat"
@@ -282,6 +282,25 @@ POST /_reindex
 --------------------------------------------------
 // AUTOSENSE
 
+By default `_reindex` uses scroll batches of 100. You can change the
+batch size with the `size` field in the `source` element:
+
+[source,js]
+--------------------------------------------------
+POST /_reindex
+{
+  "source": {
+    "index": "source",
+    "size": 1000
+  },
+  "dest": {
+    "index": "dest",
+    "routing": "=cat"
+  }
+}
+--------------------------------------------------
+// AUTOSENSE
+
 Reindex can also use the <<ingest>> feature by specifying a
 `pipeline` like this: