Add documentation about reloading search analyzers

client/rest-high-level/src/test/java/org/elasticsearch/client/RestHighLevelClientTests.java

@@ -710,8 +710,9 @@ public void testApiNamingConventions() throws Exception {
             "indices.exists_type",
             "indices.get_upgrade",
             "indices.put_alias",
+            "render_search_template",
             "scripts_painless_execute",
-            "render_search_template"
+            "indices.reload_search_analyzers"
         };
         //These API are not required for high-level client feature completeness
         String[] notRequiredApi = new String[] {

docs/reference/analysis/tokenfilters/synonym-tokenfilter.asciidoc

@@ -41,8 +41,13 @@ appear before it in the chain.
 Additional settings are:
 
 * `expand` (defaults to `true`).
+* `updateable` (defaults to false). If `true`, this marks the filter to be updateable using the 
+<<indices-reload-analyzers,analyzer reload API>>, but it will also restrict the filter to only be usable in 
+<<search-analyzer,search analyzers>>.
 * `lenient` (defaults to `false`). If `true` ignores exceptions while parsing the synonym configuration. It is important
 to note that only those synonym rules which cannot get parsed are ignored. For instance consider the following request:
+
+
 
 [source,js]
 --------------------------------------------------
@@ -181,3 +186,41 @@ error.
 If you need to build analyzers that include both multi-token filters and synonym
 filters, consider using the <<analysis-multiplexer-tokenfilter,multiplexer>> filter,
 with the multi-token filters in one branch and the synonym filter in the other.
+
+=== Updateability of search time synonyms
+
+Synonym filters that are used in <<search-analyzer,search analyzers>> can be marked
+as updateable using the `updateable` flag:
+
+[source,js]
+--------------------------------------------------
+PUT /test_index
+{
+    "settings": {
+        "index" : {
+            "analysis" : {
+                "analyzer" : {
+                    "synonym" : {
+                        "tokenizer" : "whitespace",
+                        "filter" : ["synonym"]
+                    }
+                },
+                "filter" : {
+                    "synonym" : {
+                        "type" : "synonym",
+                        "synonyms_path" : "analysis/synonym.txt",
+                        "updateable" : true
+                    }
+                }
+            }
+        }
+    }
+}
+--------------------------------------------------
+// CONSOLE
+
+Using the <<indices-reload-analyzers,analyzer reload API>>, you can trigger reloading of the
+synonym definition. The contents of the configured synonyms file will be reloaded and the
+synonyms definition the filter uses will be updated. 
+
+NOTE: Trying to use the above analyzer as an index analyzer will result in an error.

docs/reference/indices.asciidoc

@@ -56,6 +56,7 @@ index settings, aliases, mappings, and index templates.
 * <<indices-refresh>>
 * <<indices-flush>>
 * <<indices-forcemerge>>
+* <<indices-reload-analyzers>>
 
 --
 
@@ -109,3 +110,5 @@ include::indices/refresh.asciidoc[]
 
 include::indices/forcemerge.asciidoc[]
 
+include::indices/reload-analyzers.asciidoc[]
+

docs/reference/indices/reload-analyzers.asciidoc

@@ -0,0 +1,65 @@
+[[indices-reload-analyzers]]
+== Reload Search Analyzers
+
+experimental[]
+
+Reloads search analyzers and its resources.
+
+The `_reload_search_analyzers` API can be run on one or more indices and will
+reload all search analyzers that contain components that were marked as
+updateable when they were created, such as 
+<<analysis-synonym-tokenfilter,synonym token filters>>:
+
+[source,js]
+--------------------------------------------------
+PUT /test_index
+{
+    "settings": {
+        "index" : {
+            "analysis" : {
+                "analyzer" : {
+                    "my_synonyms" : {
+                        "tokenizer" : "whitespace",
+                        "filter" : ["synonym"]
+                    }
+                },
+                "filter" : {
+                    "synonym" : {
+                        "type" : "synonym",
+                        "synonyms_path" : "analysis/synonym.txt",
+                        "updateable" : true <1>
+                    }
+                }
+            }
+        }
+    },
+    "mappings": {
+        "properties": {
+            "text": {
+                "type": "text",
+                "analyzer" : "standard",
+                "search_analyzer": "my_synonyms" <2>
+            }
+        }
+    }
+}
+--------------------------------------------------
+// CONSOLE
+
+<1> Mark the synonym filter as updateable.
+<2> Synonym analyzer is usable as a search_analyzer.
+
+Calling the `_reload_search_analyzers` endpoint will now trigger reloading of the
+synonyms from the configured "synonym.txt" file.
+
+NOTE: Reloading will happen on every node the index has shards, so its important
+to update the synonym file contents on every data node (even the ones that don't currently
+hold shard copies; shards might be relocated there in the future) before calling
+reload to ensure the new state of the file is reflected everywhere in the cluster.
+
+[source,js]
+--------------------------------------------------
+POST /my_index/_reload_search_analyzers
+--------------------------------------------------
+// CONSOLE
+// TEST[s/^/PUT my_index\n/]

rest-api-spec/src/main/resources/rest-api-spec/api/indices.reload_search_analyzers.json

@@ -0,0 +1,33 @@
+{
+  "indices.reload_search_analyzers": {
+    "documentation": "https://www.elastic.co/guide/en/elasticsearch/reference/master/indices-reload-analyzers.html",
+    "stability": "experimental",
+    "methods": ["GET", "POST"],
+    "url": {
+      "paths": ["/{index}/_reload_search_analyzers"],
+      "parts": {
+        "index": {
+         "type": "list",
+         "description" : "A comma-separated list of index names to reload analyzers for"
+        }
+     },
+     "params": {
+        "ignore_unavailable": {
+            "type" : "boolean",
+            "description" : "Whether specified concrete indices should be ignored when unavailable (missing or closed)"
+        },
+        "allow_no_indices": {
+            "type" : "boolean",
+            "description" : "Whether to ignore if a wildcard indices expression resolves into no concrete indices. (This includes `_all` string or when no indices have been specified)"
+        },
+        "expand_wildcards": {
+            "type" : "enum",
+            "options" : ["open","closed","none","all"],
+            "default" : "open",
+            "description" : "Whether to expand wildcard expression to concrete indices that are open, closed or both."
+        }
+     }
+    }, 
+    "body": null
+  }
+}

server/src/main/java/org/elasticsearch/action/ActionModule.java

@@ -283,6 +283,7 @@
 import org.elasticsearch.rest.action.admin.indices.RestPutMappingAction;
 import org.elasticsearch.rest.action.admin.indices.RestRecoveryAction;
 import org.elasticsearch.rest.action.admin.indices.RestRefreshAction;
+import org.elasticsearch.rest.action.admin.indices.RestReloadAnalyzersAction;
 import org.elasticsearch.rest.action.admin.indices.RestResizeHandler;
 import org.elasticsearch.rest.action.admin.indices.RestRolloverIndexAction;
 import org.elasticsearch.rest.action.admin.indices.RestSyncedFlushAction;
@@ -608,6 +609,7 @@ public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster) {
         registerHandler.accept(new RestGetFieldMappingAction(settings, restController));
 
         registerHandler.accept(new RestRefreshAction(settings, restController));
+        registerHandler.accept(new RestReloadAnalyzersAction(settings, restController));
         registerHandler.accept(new RestFlushAction(settings, restController));
         registerHandler.accept(new RestSyncedFlushAction(settings, restController));
         registerHandler.accept(new RestForceMergeAction(settings, restController));