Since the bulk-export query can be expensive, it is advisable for sites with high throughput requirements to either schedule the Sitemap Generator for off-peak hours, or even run the Sitemap Generator against a dedicated staging index. When running the Sitemap Generator against a dedicated index, you can gain an additional performance advantage by using the QUERY_FIELD_LIST to specify the properties and dimensions that are available for display in URLs rather than enabling the properties and dimensions to display with record list.