Extensible Storage Engine - Databases

Databases

A database is both a physical and logical grouping of data. An ESE database looks like a single file to Windows. Internally the database is a collection of 2, 4, 8, 16, or 32 KB pages (16 and 32 KB page options are only available in Windows 7 and Exchange 2010), arranged in a balanced B-tree structure. These pages contain meta-data to describe the data contained within the database, data itself, indexes to persist interesting orders of the data, and other information. This information is intermixed within the database file but efforts are made to keep data used together clustered together within the database. An ESE database may contain up to 232 pages, or 16 terabytes of data, for 8 kilobyte sized pages.

ESE databases are organized into groups called instances. Most applications use a single instance, but all applications can also use multiple instances. The importance of the instance is that it associates a single recovery log series with one or more databases. Currently, up to 6 user databases may be attached to an ESE instance at any time. Each separate process using ESE may have up to 1024 ESE instances.

A database is portable in that it can be detached from one running ESE instance and later attached to the same or a different running instance. While detached, a database may be copied using standard Windows utilities. The database cannot be copied while it is being actively used since ESE opens database files exclusively. A database may physically reside on any device supported for directly-addressable I/O operations by Windows.