Tag: storage engine

• PFS Pages: How SQL Server tracks “Page Free Space”

  

  2014-04-30 - General, Series, SQL Server Internals, Storage Wednesday

  PFS pages contain information about the free space available on all pages in a database file. They contain one byte per page that also holds four additional status bits. Read on to discover how to interpret the PFS data.

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• 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 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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• The Extent (A Storage Wednesday Post)

  

  2014-03-19 - General, Series, SQL Server Internals, Storage Wednesday

  SQL Server organizes database pages in groups of 8 called extents. An extent is the smallest unit that SQL Server will reserve on disk. However, smaller tables are still possible through mixed extents. Read on to get all the details.

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