A Technical Overview of Microsoft® SQL Server™ 2005 High Availability Beta 2 Matthew Stephen IT Pro Evangelist (SQL Server) http://blogs.technet.com/mat_stephen

What We Will Cover Barriers to availability Database server failure or disaster User or application error Data access concurrency limitations

Barriers to Availability Overview Business requirements Time and location Processes Expectations Technology Hardware DBMS software Application software

Barriers to Availability Primary Server or DBMS Barriers Database failure or disaster Hardware failure Human-made disaster Natural disaster

Barriers to Availability Primary Server or DBMS Barriers User or application error Accidental data modifications Malicious data modifications Data access concurrency limitations Multiple transactions accessing same data Persistent data structure changes

Database Server Failure or Disaster Overview Failover clustering Database mirroring Peer-to-peer replication Comparison of other alternatives Standard replication topologies Log shipping Backup and restore Detach, copy, attach

Database Server Failure or Disaster Failover Clustering Provides a hot standby Built on Microsoft Cluster Services (MSCS) Multiple nodes (Now 8) Automatic failover of instance (~20 seconds) Certified hardware required Zero committed work loss Single copy of instance databases Standby not available for any other use Supports more SQL services MS-2087 Implementing Microsoft Windows 2000 Clustering

Database Server Failure or Disaster Failover Clustering Shared Disk Array 2nd Private ‘Heartbeat’ network Clustered Servers Clients Virtual Server Primary Network

Database Server Failure or Disaster Database Mirroring Provides a hot standby (instant) Database failover Very fast automatic failover (less than 3 seconds) Transparent client redirect Zero committed work loss Some performance impact Maximum one mirror for each database Standby not directly available for any other use MS-2733 Updating Your Database Administration Skills to Microsoft SQL Server 2005

Database Server Failure or Disaster Database Mirroring Hardware No special hardware required Requires a second server Servers do not need duplicate hardware Virtually no distance limitations No shared disk arrays Transaction latency requirements determine acceptable network latency MS-2733 Updating Your Database Administration Skills to Microsoft SQL Server 2005

Database Server Failure or Disaster Database Mirroring With Automatic Failover Separate Disk Arrays Principal Server Mirror Server Clients Witness Server

Database Server Failure or Disaster Database Mirroring With Automatic Failover

Database Server Failure or Disaster Peer-to-Peer Replication Provides a hot standby of publication(s) Can replicate entire database Improved performance No distance limitations Some committed data loss No conflict detection MS-2733 Updating Your Database Administration Skills to Microsoft SQL Server 2005

Database Server Failure or Disaster Fault Tolerance with Peer-to-Peer Replication

Database Server Failure or Disaster Load Balancing with Peer-to-Peer Replication

Database Server Failure or Disaster Peer-to-Peer Replication Topology

User or Application Error Comparison of High Availability Options Feature Hot Standby Warm Standby Cold Standby Database Mirroring Failover Clustering Peer-to-Peer Transactional Replication Log Shipping Backup / Restore Detach / Copy / Attach Data Loss No data loss option No data loss Some Data Loss possible Some data loss possible Some data loss likely Automatic Failover Yes Optional No Transparent to Client Yes, Auto-Redirect Yes, Reconnect to same IP No, NLB helps Downtime < 3 Seconds 20 Sec + DB Recovery None Seconds Seconds + DB Recovery Detect, Restore, Manual failover Detect, Attach, Manual failover Standby Read Access Continuously accessible Snapshot Continuously accessible Intermittently accessible

User or Application Error Comparison of High Availability Options Feature Hot Standby Warm Standby Cold Standby Database Mirroring Failover Clustering Peer-to-Peer Replication Transactional Replication Log Shipping Backup/ Restore Detach/ Copy/ Attach Data Granularity Database Only All System and User Databases Table or View Masks Disk Failure Yes No, Shared Disk Special Hardware Needed No, Dup. system needed Specialized Hardware from Cluster HCL Complexity Some More

User or Application Error Overview Database snapshots Database snapshot scenarios

User or Application Error Database Snapshots Read-only Static view of database Transaction consistent at point of time Does not store all data pages Reads only original data pages Reads data from snapshot if data has changed Reads data from database if data has not changed Increases disk I/O of source database MS-2733 Updating Your Database Administration Skills to Microsoft SQL Server 2005

User or Application Error How Database Snapshots Work

User or Application Error Database Snapshot Scenarios Enabling mirroring database for reporting Historical point-in-time reporting Recovering from administrative error Protecting against application or user error

Data Access Concurrency Limitations Overview Pessimistic concurrency controls Optimistic concurrency controls Snapshot isolation level Read committed (Snapshot) ONLINE index operations

Data Access Concurrency Limitations Pessimistic Concurrency Controls Default Setting and Behavior Designed for Data Integrity SELECT Operations Require Shared Resource Locks Different Isolation Levels Control Behavior of Shared Locks MS-2072 Administering a Microsoft SQL Server 2000 Database

Data Access Concurrency Limitations Optimistic Concurrency Controls Optional setting and behavior Implemented using row versioning Designed for data integrity but allows reads of committed data SELECT operations do not require shared resource locks Different isolation levels control behavior of committed reads

Data Access Concurrency Limitations Row Versioning Several Uses Triggers for Inserted and Deleted tables Multiple Active Result Sets (MARS) sessions ONLINE Index Operations Optimistic concurrency controls (row snapshots) Versions built in tempdb for all modified rows Versions deleted when no remaining transaction or operation needs them

Data Access Concurrency Limitations Snapshot Isolation Level Reads committed data at time of transaction start ALLOW _SNAPSHOT_ISOLATION database option TRANSACTION ISOLATION LEVEL SNAPSHOT session option

Data Access Concurrency Limitations Read Committed (Snapshot) Reads committed data at time of statement READ_COMMITTED_SNAPSHOT database option TRANSACTION ISOLATION LEVEL READ COMMITTED session option

Data Access Concurrency Limitations ONLINE Index Operations Table accessible for reads and modifications during ONLINE index operations Existing non-clustered indexes available to optimize during ONLINE clustered index operations Non-clustered index is not available during its index operation

Data Access Concurrency Limitations ONLINE Index Operation Commands CREATE INDEX ALTER INDEX DROP INDEX ALTER TABLE ADD or DROP of UNIQUE index ADD or DROP of PRIMARY KEY with CLUSTERED index option

Data Access Concurrency Limitations ONLINE Clustered Index Creation Operation

Session Summary Several new features available in SQL Server 2005 to protect against server failure Database snapshots can be used to protect against application, user, or administrative error Use the new optimistic concurrency controls and ONLINE index operations to reduce database contention issues