Issue #2850684 by daffie, RoSk0: Default Database Schema::fieldExists() is slow for PostgreSQL

core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php

@@ -628,6 +628,15 @@ public function fieldSetNoDefault($table, $field) {
     $this->connection->query('ALTER TABLE {' . $table . '} ALTER COLUMN "' . $field . '" DROP DEFAULT');
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function fieldExists($table, $column) {
+    $prefixInfo = $this->getPrefixInfo($table);
+
+    return (bool) $this->connection->query("SELECT 1 FROM pg_attribute WHERE attrelid = :key::regclass AND attname = :column AND NOT attisdropped AND attnum > 0", array(':key' => $prefixInfo['schema'] . '.' . $prefixInfo['table'], ':column' => $column))->fetchField();
+  }
+
   /**
    * {@inheritdoc}
    */