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Certain search engine services may require an extended period of time for inclusion, which is seen as a delay and a frustration by website administrators who wish to have their websites appear in search engine results.
Delayed inclusion may due to the size of the index that the service must maintain or due to corporate, political or social policies. Some services only index content collected by a crawler program which does not allow for manual adding of content to index.
A criticism of instant indexing is that certain services filter results manually or via algorithms that prevent instant inclusion to avoid inclusion of content that violates the service's policies.
Instant indexing impacts the timeliness of the content included in the index. Given the manner in which many crawlers operate in the case of Internet search engines, websites are only visited if a some other website links to them. Unlinked web sites are never visited (see invisible web) by the crawler because it cannot reach the website during its traversal. It is assumed that unlinked websites are less authoritative and less popular, and therefore of less quality. Over time, if a website is popular or authoritative, it is assumed that other websites will eventually link to it. If a search engine service provides instant indexing, it bypasses this quality control mechanism by not requiring incoming links. This infers that the search engine's service produces lower quality results.