What is the concept of ghosting and unghosting in SharePoint?

In SharePoint most of the site pages derive from templates. The custom pages only store the difference between them. The template is loaded in memory and applied to the custom pages on fly. In other words the template is stored in a cache. This definitely brings in performance and flexibility.  Flexibility is in terms that when we change the template page it's applied to all custom pages. These pages are loaded from the file system. So pages which are loaded from the file system are termed as ghosted pages.

If the page data is loaded from the content database it's termed as unghosted pages.

As a note, let me clarify the concept of document and content table as we are already trying to understand the concept of ghosting and unghosting. As we know that SharePoint stores all pages in the database. Looking from a 50,000 feet it has two tables one is the document table which has the entry of page and the other is the content which has the source code of the ASPX page.

So, when a page is requested it first checks in the document table and then goes to the content table to load the page. If it does not find data of the page it goes to the file directory to load the page. This loading is done by ASP.NET runtime himself. But if there is data present in the content table then it's loaded by the 'safe mode parser.

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