Fatal error: Uncaught Error: Class "DatabaseConnection_mysql" not found in /var/www/html/includes/database/database.inc:1796
Stack trace:
#0 /var/www/html/includes/database/database.inc(1582): Database::openConnection('default', 'default')
#1 /var/www/html/includes/database/database.inc(2687): Database::getConnection()
#2 /var/www/html/includes/cache.inc(359): db_escape_table('cache_bootstrap')
#3 /var/www/html/includes/cache.inc(340): DrupalDatabaseCache->getMultiple(Array)
#4 /var/www/html/includes/cache.inc(57): DrupalDatabaseCache->get('lookup_cache')
#5 /var/www/html/includes/bootstrap.inc(3535): cache_get('lookup_cache', 'cache_bootstrap')
#6 /var/www/html/includes/bootstrap.inc(3492): _registry_check_code('class', 'DatabaseConnect...')
#7 /var/www/html/includes/database/database.inc(1796): drupal_autoload_class('DatabaseConnect...')
#8 /var/www/html/includes/database/database.inc(1582): Database::openConnection('default', 'default')
#9 /var/www/html/includes/database/database.inc(2687): Database::getConnection()
#10 /var/www/html/includes/cache.inc(359): db_escape_table('cache_bootstrap')
#11 /var/www/html/includes/cache.inc(340): DrupalDatabaseCache->getMultiple(Array)
#12 /var/www/html/includes/cache.inc(57): DrupalDatabaseCache->get('module_implemen...')
#13 /var/www/html/includes/module.inc(763): cache_get('module_implemen...', 'cache_bootstrap')
#14 /var/www/html/includes/module.inc(963): module_implements('system_theme_in...')
#15 /var/www/html/modules/system/system.module(2531): module_invoke_all('system_theme_in...')
#16 /var/www/html/includes/theme.inc(798): _system_rebuild_theme_data()
#17 /var/www/html/includes/theme.maintenance.inc(57): list_themes()
#18 /var/www/html/includes/bootstrap.inc(2965): _drupal_maintenance_theme()
#19 /var/www/html/includes/errors.inc(177): drupal_maintenance_theme()
#20 /var/www/html/includes/bootstrap.inc(2690): _drupal_log_error(Array, true)
#21 [internal function]: _drupal_exception_handler(Object(ParseError))
#22 {main}
  thrown in /var/www/html/includes/database/database.inc on line 1796