diff --git a/lib/classes/lock/postgres_lock_factory.php b/lib/classes/lock/postgres_lock_factory.php
index de1be0815bf..0d48eaafd7b 100644
--- a/lib/classes/lock/postgres_lock_factory.php
+++ b/lib/classes/lock/postgres_lock_factory.php
@@ -33,9 +33,8 @@ defined('MOODLE_INTERNAL') || die();
  * Postgres locking implementation using advisory locks. Some important points. Postgres has
  * 2 different forms of lock functions, some accepting a single int, and some accepting 2 ints. This implementation
  * uses the 2 int version so that it uses a separate namespace from the session locking. The second note,
- * is because postgres uses integer keys for locks, we first need to map strings to a unique integer. This is
- * done by storing the strings in the lock_db table and using the auto-id returned. There is a static cache for
- * id's in this function.
+ * is because postgres uses integer keys for locks, we first need to map strings to a unique integer. This is done
+ * using a prefix of a sha1 hash converted to an integer.
  *
  * @package   core
  * @category  lock
@@ -127,44 +126,20 @@ class postgres_lock_factory implements lock_factory {
     }
 
     /**
-     * This function generates the unique index for a specific lock key.
-     * Once an index is assigned to a key, it never changes - so this is
-     * statically cached.
+     * This function generates the unique index for a specific lock key using
+     * a sha1 prefix converted to decimal.
      *
      * @param string $key
      * @return int
      * @throws \moodle_exception
      */
     protected function get_index_from_key($key) {
-        if (isset(self::$lockidcache[$key])) {
-            return self::$lockidcache[$key];
-        }
 
-        $index = 0;
-        $record = $this->db->get_record('lock_db', array('resourcekey' => $key));
-        if ($record) {
-            $index = $record->id;
-        }
-
-        if (!$index) {
-            $record = new \stdClass();
-            $record->resourcekey = $key;
-            try {
-                $index = $this->db->insert_record('lock_db', $record);
-            } catch (\dml_exception $de) {
-                // Race condition - never mind - now the value is guaranteed to exist.
-                $record = $this->db->get_record('lock_db', array('resourcekey' => $key));
-                if ($record) {
-                    $index = $record->id;
-                }
-            }
-        }
-
-        if (!$index) {
-            throw new \moodle_exception('Could not generate unique index for key');
-        }
-
-        self::$lockidcache[$key] = $index;
+        // A prefix of 7 hex chars is chosen as fffffff is the largest hex code
+        // which when converted to decimal (268435455) fits inside a 4 byte int
+        // which is the second param to pg_try_advisory_lock().
+        $hash = substr(sha1($key), 0, 7);
+        $index = hexdec($hash);
         return $index;
     }