public function getActionReferenceColumnsByTable()
    {
        $result = array(
            'log_link_visit_action' => array('idaction_url',
                'idaction_url_ref',
                'idaction_name_ref'
            ),

            'log_conversion'        => array('idaction_url'),

            'log_visit'             => array('visit_exit_idaction_url',
                'visit_exit_idaction_name',
                'visit_entry_idaction_url',
                'visit_entry_idaction_name'),

            'log_conversion_item'   => array('idaction_sku',
                'idaction_name',
                'idaction_category',
                'idaction_category2',
                'idaction_category3',
                'idaction_category4',
                'idaction_category5')
        );

        $dimensionIdActionColumns = $this->getVisitActionTableActionReferences();
        $result['log_link_visit_action'] = array_unique(
            array_merge($result['log_link_visit_action'], $dimensionIdActionColumns));

        foreach ($this->actionReferenceColumnsOverride as $table => $columns) {
            if (empty($result[$table])) {
                $result[$table] = $columns;
            } else {
                $result[$table] = array_unique(array_merge($result[$table], $columns));
            }
        }

        /**
         * Triggered when detecting which log_action entries to keep. Any log tables that use the log_action
         * table to reference text via an ID should add their table info so no actions that are still in use
         * will be accidentally deleted.
         *
         * **Example**
         *
         *     Piwik::addAction('Db.getActionReferenceColumnsByTable', function(&$result) {
         *         $tableNameUnprefixed = 'log_example';
         *         $columnNameThatReferencesIdActionInLogActionTable = 'idaction_example';
         *         $result[$tableNameUnprefixed] = array($columnNameThatReferencesIdActionInLogActionTable);
         *     });
         * @param array $result
         */
        Piwik::postEvent('Db.getActionReferenceColumnsByTable', array(&$result));

        return $result;
    }