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Archive for October 12, 2011

What are Records, Pages, Extents, Heap in SQL Server?

October 12, 2011 1 comment

 
I found this very interesting series by Paul Randal on some basic terms of SQL Server Storage Engine at MSDN SQL Server blog. This is a 4 part series and provides information on records, pages, extents and heap structures.

I’ve seen many people asking questions related to these topics on MSDN & other SQL Server forums. And there are very few tech articles on internet and MS BOL regarding these. Paul has very breifly and in layman terms explained these topics.
 

I’d like to share the following topics for my future reference and for my blog viewers:

Part 1. What are Rows/Records?

Part 2. What are Pages?

Part 3. What are Extents?

Part 4. What is a Heap?
 

–> PAGE: A page in SQL Server is an 8 KB data storage area. There are 8 types of pages:

1. Data page
2. Index page
3. IAM (Index Allocation Map) page
4. GAM (Global Allocation Map) and SGAM (Shared Global Allocation Map) page
5. PFS (Page Free Space) page
6. Text/Image page
7. Sort page
8. Differential Bitmap page
9. Bulk-Changed Map page
10. Boot page
11. FileHeader page


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Categories: DB Concepts Tags: , , ,