Download Wiley Microsoft SQL Server 2005 For Dummies

30
Part I: SQL Server 2005: An Overview
Concurrent data access
Concurrent data access is about getting to data when others are also accessing it:
⻬ Database snapshots: Creates a logical copy of a database at a specific
point in time. You can use snapshots as the basis for Reporting Services
reports without putting a load on the live copy of the database.
⻬ Snapshot isolation: This is a new transaction isolation level that
improves availability for read applications, because writes do not block
reads. Write applications are subject to mandatory conflict detection.
⻬ Online Indexing: During the time that an index is being rebuilt, it
remains possible to use the index for accessing data. This is likely to
improve performance during that period.
Availability after server failure
SQL Server 2005 provides better availability in scenarios relating to server
failure or some other catastrophic situation. The following features are additional to server failover clustering that was supported in SQL Server 2000
Enterprise edition:
⻬ Faster Recovery: After a server failure, databases are made available to
users more quickly during the recovery process, which improves availability.
⻬ Database Mirroring: Using standard hardware, a mirror server always
maintains an up-to-date copy of the database. On failure of the principal
server, the mirror server is available within three seconds, making the
server failure invisible to users.
⻬ Transparent Client Redirect: Under the covers, Database Mirroring uses
Transparent Client Redirect. The MDAC (Microsoft Data Access
Components) layer notes the mirror server when connecting to a principal server. If the principal server fails, MDAC redirects the connection to
the mirror server.
Availability during database maintenance
The backup and restore process must be reliable if you are to restore a database effectively, such as after a hardware failure. Here are the relevant features of SQL Server 2005: