What are the scenarios where full crawl will required

What are the scenarios where full crawl will required

Description: Before users can perform searches in SharePoint Server 2013, we must crawl or federate the content that want to be able to search. When you crawl content, the Search service builds a search index that users can run queries (search requests) against. You can also configure the Search system to display search results from an external provider (such as Bing) alongside the results from the local search index. The process of getting search results from an external provider and displaying the results locally is called federation. 

crawl will required in below:

Reasons for a Search service application administrator to do a full crawl for one or more content sources include the following. In All the below we need to do a full crawl to get the data search.

1.     A Search service application has just been created and the preconfigured content source Local SharePoint sites has not been crawled yet.

2.     Some other content source is new and has not been crawled yet.

3.     The Search service application administrator has changed a content source.

4.     A software update or service pack was installed on servers in the farm. See the instructions for the software update or service pack for more information.

5.     A Search service application administrator or site collection administrator added or changed a managed property. A full crawl of all affected content sources is required for the new or changed managed property to take effect.

6.     You want to detect security changes that were made to local groups on a file share after the last full crawl of the file share.

7.     You want to resolve consecutive incremental crawl failures. If an incremental crawl fails a large number of consecutive times for any particular content, the system removes the affected content from the search index.

8.     Crawl rules have been added, deleted, or modified.

9.     You want to replace a corrupted search index.

10.  The permissions for the user account that is assigned to the default content access account have changed.

The system does a full crawl even when an incremental crawl or continuous crawl is scheduled under the following circumstances:

1.     A search administrator stopped the previous crawl.

2.     A content database was restored, or a farm administrator has detached and reattached a content database.

3.     A full crawl of the content source has never been done from this Search service application.

4.     The crawl database does not contain entries for the addresses that are being crawled. Without entries in the crawl database for the items being crawled, incremental crawls cannot occur.

 

I hope the above information will help you to resolve the issue, in case of any queries/questions regarding the above mentioned information then please let me know. I would be more than happy to help you as well as resolves your issues, Thank you.