Manually request crawling and reindexing of a site, a library or a list
In SharePoint, content is automatically crawled based on a defined crawl schedule. The crawler picks up content that has changed since the last crawl and updates the index. You will want to manually request crawling and full reindexing of a site, a document library, or a list after a schema change has occurred.
Reindexing a site can cause a massive load on the search system. Don't reindex your site unless you've made changes that require all items to be reindexed.
Reindex after changing managed properties
When people search for content on your SharePoint sites, what's in your search index decides what they'll find. The search index contains information from all documents and pages on your site.
The search index is built up by crawling the content on your SharePoint site. The crawler picks up content and metadata from the documents in the form of crawled properties. To get the content and metadata from the documents into the search index, the crawled properties must be mapped to managed properties. Only managed properties are kept in the index. This means that users can only search on managed properties.
When you've changed a managed property, or when you've changed the mapping of crawled and managed properties, the site must be recrawled before your changes will be reflected in the search index. Because your changes are made in the search schema, and not to the actual site, the crawler won't automatically reindex the site. To make sure that your changes are crawled and fully reindexed, you must request a reindexing of the site. The site content will be recrawled and reindexed so that you can start using the managed properties in queries, query rules and display templates.
You can also choose to only reindex a document library or a list. When you've changed a managed property that's used in a library or list, or changed the mapping of crawled and managed properties, you can specifically request a reindexing of that library or list only. All of the content in that library or list is marked as changed, and the content is picked up during the next scheduled crawl and reindexed.
Learn more about search and crawled and managed properties in Manage the search schema in SharePoint.
Reindex a site
On the site, select Settings , and then select Site settings. If you don't see Site settings, select Site information, and then select View all site settings.
Under Search, click Search and offline availability.
In the Reindex site section, click Reindex site.
A warning appears, click Reindex site again to confirm. The content will be reindexed during the next scheduled crawl.
Reindex a document library or a list
On the site, go to the list or library that you want to reindex.
In the ribbon, click the Library tab or the List tab.
In the Library ribbon, choose Library Settings. Or, in the List ribbon, choose List Settings.
On the Settings page, under General Settings, choose Advanced settings.
Scroll down to Reindex Document Library or Reindex List, and click the button. The content will be reindexed during the next scheduled crawl.