diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index a912b10efc56..a1c2123d538c 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -2357,6 +2357,16 @@ public function list_participants($currentgroup, $idsonly, $tablesort = false) {
                            $additionalfilters
                   ORDER BY $orderby";
 
+            $records = $DB->get_records_sql("EXPLAIN $sql", $params);
+            foreach ($records as $record) {
+                echo "<!--\n" . print_r($record, true) . "\n-->\n";
+            }
+
+            $records = $DB->get_records_sql("EXPLAIN ANALYZE $sql", $params);
+            foreach ($records as $record) {
+                echo "<!--\n" . print_r($record, true) . "\n-->\n";
+            }
+
             $users = $DB->get_records_sql($sql, $params);
 
             $cm = $this->get_course_module();