What is the page in SQL Server?

What is the page in SQL Server?

The page is the fundamental unit of data storage in SQL Server. An extent is a collection of eight physically contiguous pages. Extents help efficiently manage pages. This guide describes the data structures that are used to manage pages and extents in all versions of SQL Server.

What are SQL Server extents?

Extents are the basic unit in which space is allocated to tables and indexes. An extent is 8 contiguous pages, or 64 KB. This means SQL Server 2000 databases have 16 extents per megabyte. To make its space allocation efficient, SQL Server 2000 does not allocate entire extents to tables with small amounts of data.

How many types of pages are there in SQL Server?

As far as I know, there are about 14 types of pages in SQL Server data file. Type 1 – Data page. Small LOB value(s), multiple types and rows.

What is a GAM page?

GAM pages are used by SQL Server to track, which extents are in use and which ones are unallocated. Each GAM page contains a 7988-byte bitmap covering all extent in a single GAM interval of 511232 pages. Each bit corresponds to a single extent, and a value of 1 indicates that that extent is still unallocated.

What is a page in database?

A page is a unit of storage whose size is configurable on a system-wide, database-wide, or conglomerate-specific basis. By default, a conglomerate grows one page at a time until eight pages of user data (or nine pages of total disk use, which includes one page of internal information) have been allocated.

What are database extents?

An extent is a logical unit of database storage space allocation made up of a number of contiguous data blocks. Each segment is composed of one or more extents. When the existing space in a segment is completely used, Oracle allocates a new extent for the segment.

What is boot page in SQL Server?

Well, each and every SQL Server database has something called “Boot Page” where it stores all the metadata related to the respective database and the boot page will be always 9th page of the 1st file in a database.

What is GAM and SGAM in SQL Server?

When we create a database, the data files will be logically divided into the pages and extents. Later, when user objects are created, the pages are allocated to them to store the data. GAM (Global Allocation Map) and SGAM (Shared Global Allocation Map) pages are used to track the space allocation in SQL Server.

How many types of pages are available in SQL?

How many extents can a single segment use?

No matter what type, each segment in a database is created with at least one extent to hold its data. This extent is called the segment’s initial extent. Note: Rollback segments always have at least two extents.