Microsoft® SQL Server 2012 Unleashed

Index Allocation Map Pages

Index allocation map (IAM) pages keep track of the extents used by a heap or index. Each heap table and index has at least one IAM page for each file where it has extents. An IAM cannot reference pages in other database files; if the heap or index spreads to a new database file, a new IAM for the heap or index is created in that file. IAM pages are allocated as needed and are spread randomly throughout the database files.

An IAM page contains a small header that has the address of the first extent in the range of pages being mapped by the IAM. It also contains eight page pointers that keep track of index or heap pages that are in mixed extents. These pointers might or might not contain any information, depending on ...