Mark searcher as accessed in acquireSearcher (#41335)

This fixes an issue where every N seconds a slow search request is triggered
since the searcher access time is not set unless the shard is idle. This change
moves to a more pro-active approach setting the searcher as accessed all the time.

server/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -1215,6 +1215,7 @@ private void markSearcherAccessed() {
 
     private Engine.Searcher acquireSearcher(String source, Engine.SearcherScope scope) {
         readAllowed();
+        markSearcherAccessed();
         final Engine engine = getEngine();
         final Engine.Searcher searcher = engine.acquireSearcher(source, scope);
         assert ElasticsearchDirectoryReader.unwrap(searcher.getDirectoryReader())
@@ -2983,9 +2984,7 @@ private void setRefreshPending(Engine engine) {
      *                 <code>true</code> if the listener was registered to wait for a refresh.
      */
     public final void awaitShardSearchActive(Consumer<Boolean> listener) {
-        if (isSearchIdle()) {
-            markSearcherAccessed(); // move the shard into non-search idle
-        }
+        markSearcherAccessed(); // move the shard into non-search idle
         final Translog.Location location = pendingRefreshLocation.get();
         if (location != null) {
             addRefreshListener(location, (b) -> {

server/src/test/java/org/elasticsearch/index/shard/IndexShardTests.java

@@ -3234,6 +3234,12 @@ public void testIsSearchIdle() throws Exception {
             // now loop until we are fast enough... shouldn't take long
             primary.awaitShardSearchActive(aBoolean -> {});
         } while (primary.isSearchIdle());
+
+        assertBusy(() -> assertTrue(primary.isSearchIdle()));
+        do {
+            // now loop until we are fast enough... shouldn't take long
+            primary.acquireSearcher("test").close();
+        } while (primary.isSearchIdle());
         closeShards(primary);
     }