Category: Storage Wednesday

• The Shared Global Allocation Map (SGAM)

  

  2014-04-23 - General, Series, SQL Server Internals, Storage Wednesday

  Discover how SQL Server tracks mixed extents containing free pages using a Shared Global Allocation Map made up of one SGAM page per GAM Interval.

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• The Global Allocation Map (GAM)

  

  2014-04-16 - General, Series, SQL Server Internals, Storage Wednesday

  SQL Server uses the Global Allocation Map (GAM) to catalog if an extent is allocated or not. In a 7988-byte bitmap each extent is associated with a single bit to convey that information. Read on to get all the details.

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• The GAM Interval and GAM Extents

  

  2014-04-09 - General, Series, SQL Server Internals, Storage Wednesday

  What is a GAM extent in SQL Server? What is a GAM Interval and how big is it really? Read on now to get the answers to these questions and see why a GAM interval is not 64000 extents.

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• The Index Allocation Map (IAM)

  

  2014-04-02 - General, Series, SQL Server Internals, Storage Wednesday

  SQL Server tracks the pages that belong to an allocation unit through special index allocation map pages, also called IAM pages. Each IAM page covers a single GAM-interval of the database file. All IAM pages of a single allocation unit together build an IAM-chain. Read on to find out more.

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• The Allocation Unit

  

  2014-03-26 - DMVs & CVs, General, Series, SQL Server Internals, Storage Wednesday

  SQL Server groups all pages that belong to a single partition of a single index or heap into logical units. These units are called allocation units. Read on to learn about the different types of allocation units and discover how to identify the allocation units belonging to a table.

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