Stop unnecessary index exists checks on _edit_lock meta updates

The _edit_lock meta key is not indexed, so there is no need to check if ES index exists.
This change removes the unnecessary index exists checks to reduce load on ES server.

search/includes/classes/class-search.php

@@ -631,6 +631,7 @@ protected function setup_hooks() {
 		add_filter( 'ep_post_tax_excluded_wp_query_root_check', [ $this, 'exclude_es_query_reserved_names' ] );
 
 		add_filter( 'ep_sync_indexable_kill', [ $this, 'do_not_sync_if_no_index' ], PHP_INT_MAX, 2 );
+		add_filter( 'ep_skip_post_meta_sync', [ $this, 'do_not_sync_if_no_index_for_post' ], PHP_INT_MAX, 4 );
 
 		// Store last processed id into option and clean up before & after indexing command
 		add_action( 'ep_cli_post_bulk_index', [ $this, 'update_last_processed_post_id_option' ] );
@@ -2218,9 +2219,42 @@ public function exclude_es_query_reserved_names( $taxonomies ) {
 	 */
 	public function do_not_sync_if_no_index( $kill, $indexable_slug ) {
 		$indexable = \ElasticPress\Indexables::factory()->get( $indexable_slug );
+		// @see do_not_sync_if_no_index_for_post
+		if ( 'post' === $indexable->slug ) {
+			return $kill;
+		}
+
 		if ( $indexable && ! $indexable->index_exists() ) {
 			$kill = true;
 		}
+
+		return $kill;
+	}
+
+	/**
+	 * Do not sync if no index exists for post.
+	 *
+	 * Skip triggering index exists check for _edit_lock meta key.
+	 * Less requests made to the ES server.
+	 * @see https://github.com/10up/ElasticPress/pull/1899
+	 *
+	 * @param {boolean} $kill Whether to kill the sync or not.
+	 * @param {WP_Post} $post Post object.
+	 * @param {int} $meta_id Meta ID.
+	 * @param {string} $meta_key Meta key.
+	 *
+	 * @return bool
+	 */
+	public function do_not_sync_if_no_index_for_post( $kill, $post, $meta_id, $meta_key ) {
+		if ( '_edit_lock' === $meta_key ) {
+			return true;
+		}
+
+		$indexable = \ElasticPress\Indexables::factory()->get( 'post' );
+		if ( $indexable && ! $indexable->index_exists() ) {
+			$kill = true;
+		}
+
 		return $kill;
 	}