SQL Server IAM page
SQL Server IAM page Hi Guys, Welcome to SQL Server allocation series, hope you enjoy the post1 and post2 . Today, I’m going to show you the detail of IAM page. An Index Allocation Map (IAM) page maps the extents in a 4-GB part of a database file used by an allocation unit. An allocation unit is one of three types: IN_ROW_DATA Holds a partition of a heap or index. LOB_DATA Holds large object (LOB) data types, such as XML, VARBINARY(max), and VARCHAR(max). ROW_OVERFLOW_DATA Holds variable length data stored in VARCHAR, NVARCHAR, VARBINARY, or SQL_VARIANT columns that exceed the 8,060 byte row size limit. Each partition of a heap or index contains at least an IN_ROW_DATA allocation unit. It may also contain a LOB_DATA or ROW_OVERFLOW_DATA allocation unit, depending on the heap or index schema. An IAM page covers a 4-GB range in a file and is the same coverage as a GAM or SGAM page. If the allocation unit contains extents from more than one file, or more than one 4-GB range of a file, t