Pro SQL Server 2012 Administration by Ken Simmons Sylvester Carstarphen

Author:Ken Simmons, Sylvester Carstarphen
Language: eng
Format: epub, pdf
Publisher: Apress®
Published: 2012-05-08T16:00:00+00:00

Figure 9-2. The nonclustered indexes with pointers to the clustered index

Heap Structure

We would like to briefly mention the structure of heaps in this section. Unlike clustered and nonclustered indexes, the data stored within a heap table has no structure. The data stored within a heap table is linked by the index allocation map (IAM) pages that are allocated for the object. Internal system object points to the first IAM page where the data is stored. Because of the lack of order within the heap, SQL Server has to scan each page of the entire heap to determine what data meets the criteria of any given query. Because of this, table scans on heaps are often times inefficient. You should avoid scans on heaps as much as possible, especially on large tables.

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