Microsoft® SQL Server 2012 Unleashed

Page Free Space Pages

A page free space (PFS) page records whether each page is allocated and the amount of free space available on the page. Each PFS covers 8,088 contiguous pages in the file. For each of the 8,088 pages, the PFS has a 1-byte record that contains a bitmap for each page indicating whether the page is empty, 1 to 50% full, 51 to 80% full, 81 to 95% full, or more than 95% full. The first PFS page in a file is located at page number 1, the second PFS page is located at page 8088, and each additional PFS page is located every 8,088 pages after that. SQL Server uses PFS pages to find free pages on extents and to find pages with space available on extents when a new row needs to be added to a table or index.

Figure 30.6 shows the layout ...