Microsoft® SQL Server® 2008 Internals

Allocation Consistency Checks

These checks verify the contents of and relationships between the various structures that track page and extent allocations in the database. The structures involved are as follows:

• PFS pages, which track the allocation status of individual pages within a 64-MB section of a data file (a PFS interval)

• GAM pages, which track the allocation status of all extents within a 4-GB section of a data file (a GAM interval)

• SGAM pages, which track all mixed extents that have at least one page available for allocation with a GAM interval

• IAM pages, which track all pages and extents allocated to an allocation unit from a GAM interval

• IAM chains, which are a linked-list of all IAM pages for an allocation unit (and hence track all pages ...