This functionality was removed in VuFind 4.0; it is recommended that you use Google Analytics or Piwik to collect usage data.
VuFind's statistic gathering functionality can read and write data in the database or Solr index (and also has write-only file capabilities). You can write custom plugins to use other statistics-gathering mechanisms.
Key Plugin Details
Default Namespace: \VuFind\Statistics\Driver
Base Class: \VuFind\Statistics\Driver\AbstractBase
Service Locator Configuration Section in module.config.php: ['vufind']['plugin_managers']['statistics_driver']
Service Manager Name for Service Locator: VuFind\StatisticsDriverPluginManager
See the General Plugin Information page for more details on VuFind plugins.