Building Highly Available Systems with SQL Server™ 2005 Vineet Gupta Evangelist – Data and...

Building Highly Available Systems with SQL Server™ 2005

Building Highly Available Systems with SQL Server™ 2005

Vineet GuptaVineet GuptaEvangelist – Data and IntegrationEvangelist – Data and IntegrationMicrosoft Corp.Microsoft Corp.

AvailabilityAvailabilityWhat does it mean to you?What does it mean to you?

Why not?Why not? Site is unavailableSite is unavailable System is unavailableSystem is unavailable Database is unavailableDatabase is unavailable Database is Database is partially unpartially unavailableavailable Table is unavailableTable is unavailable Data is unavailableData is unavailable

Can your customers get done, Can your customers get done, what they need to get done, what they need to get done,

when they need to do it?when they need to do it?

24x7x36524x7x365

Barriers To AvailabilityBarriers To Availability

Database Maintenance and Database Maintenance and OperationsOperations

Data Access Concurrency LimitationsData Access Concurrency Limitations Database Server Failure or DisasterDatabase Server Failure or Disaster

Barriers To AvailabilityBarriers To Availability Database Maintenance and Database Maintenance and

OperationsOperations Fast RecoveryFast Recovery Partial AvailabilityPartial Availability Online RestoreOnline Restore Media ReliabilityMedia Reliability Dedicated Administration ConnectionDedicated Administration Connection Dynamic ConfigurationDynamic Configuration

Data Access Concurrency LimitationsData Access Concurrency Limitations Database Server Failure or DisasterDatabase Server Failure or Disaster

What happens when…What happens when…

Disks FailDisks Fail In SQL ServerIn SQL Server™™ 2000 2000

Database is marked suspect Database is marked suspect Users are unable to access the databaseUsers are unable to access the database

In SQL ServerIn SQL Server™™ 2005 2005 Filegroup is marked offlineFilegroup is marked offline Users are able to access undamaged dataUsers are able to access undamaged data

Partial Database AvailabilityPartial Database AvailabilityImproving Availability for Isolated Improving Availability for Isolated DisasterDisaster Undamaged data remains available Undamaged data remains available

while damaged data is inaccessiblewhile damaged data is inaccessible File Status shown in File Status shown in

sys.database_files catalog viewsys.database_files catalog view Page Errors written to suspect_pages Page Errors written to suspect_pages

table in msdbtable in msdb Agent alerts:Agent alerts:

Notification of the damaged fileNotification of the damaged file Can take the database offline, if desiredCan take the database offline, if desired Can automate the restore, for read-only Can automate the restore, for read-only

datadata


Recovery beginsRecovery begins In SQL ServerIn SQL Server™™ 2000 2000

DatabaseDatabase is in a restoring state is in a restoring state Users are Users are unableunable to access the database to access the database File needs to be recreated and zero File needs to be recreated and zero

initializedinitialized File Restore can proceed – File Restore can proceed – offlineoffline

In SQL ServerIn SQL Server™™ 2005 2005 FilegroupFilegroup is in a restoring state is in a restoring state Users are Users are ableable to access undamaged data to access undamaged data File can be recreated with instant file File can be recreated with instant file

InitializationInitialization Piecemeal Restore can proceed – Piecemeal Restore can proceed – online online

Online Piecemeal RestoreOnline Piecemeal RestoreImproving Availability during RecoveryImproving Availability during Recovery Almost any component (page, file, Almost any component (page, file,

filegroup) can be restored – ONLINEfilegroup) can be restored – ONLINE If a page is damaged – restore only that If a page is damaged – restore only that

page from a file, filegroup or database page from a file, filegroup or database backupbackup

If a file is damaged – restore only that file If a file is damaged – restore only that file from a file, filegroup or database backupfrom a file, filegroup or database backup

If a filegroup is damaged – restore only If a filegroup is damaged – restore only that filegroup from a filegroup or database that filegroup from a filegroup or database backupbackup

Readonly filegroups can be restored Readonly filegroups can be restored without rolling forward log changeswithout rolling forward log changes

Users can access the database during the Users can access the database during the restorerestore

Partial Database AvailabilityOnline Piecemeal RestorePartial Database AvailabilityOnline Piecemeal Restore

Summary: Maintenance and Summary: Maintenance and OpsOpsTechnologyTechnology ImprovesImproves WhenWhen

Partial Partial Database Database

AvailabilityAvailability

Data AvailabilityData AvailabilityUndamaged data/partitions remains Undamaged data/partitions remains

availableavailable Recovery TimeRecovery Time

Recover only that which is damagedRecover only that which is damaged

Upgrade Upgrade ImmediateImmediate

Instant File Instant File InitializatioInitializatio

nn

Database Creation TimeDatabase Creation TimeFiles are not zero-initialized Files are not zero-initialized

File, Filegroup, and Database File, Filegroup, and Database RestoreRestore

Missing files are created quicklyMissing files are created quickly Autogrow and Manual Growth Autogrow and Manual Growth

timetimeAdditional space is quickly addedAdditional space is quickly added Recovery Time Recovery Time – Less time to – Less time to

create filescreate files


Online Online Piecemeal Piecemeal RestoreRestore

Data AvailabilityData Availability Undamaged data/partitions remains Undamaged data/partitions remains

available during recoveryavailable during recovery Recovery TimeRecovery Time

Recover only that which is damaged – Recover only that which is damaged – onlineonline




Data Access Concurrency LimitationsData Access Concurrency Limitations Snapshot IsolationSnapshot Isolation Online Index OperationsOnline Index Operations ReplicationReplication Data PartitioningData Partitioning

Database Server Failure or DisasterDatabase Server Failure or Disaster


Indexes need to be rebuiltIndexes need to be rebuilt In SQL Server™ 2000In SQL Server™ 2000

Index rebuilds require an exclusive table-Index rebuilds require an exclusive table-level lock, resulting in offline rebuildslevel lock, resulting in offline rebuilds

Users are Users are unableunable to access the table to access the table

In SQL Server™ 2005In SQL Server™ 2005 Rebuilds of an index can be performed online Rebuilds of an index can be performed online

if a few simple criteria are metif a few simple criteria are met Users are Users are able able to access the tableto access the table

Online Index OperationsOnline Index OperationsImproving Concurrency during Index Improving Concurrency during Index MaintenanceMaintenance SQL Server™ 2000SQL Server™ 2000

Offline Index RebuildsOffline Index Rebuilds; table data is ; table data is unavailable during operationunavailable during operation

Rebuild options: DBCC DBREINDEX and CREATE Rebuild options: DBCC DBREINDEX and CREATE with DROP_EXISTINGwith DROP_EXISTING

SQL Server™ 2005SQL Server™ 2005 Includes all of the above offline operations, Includes all of the above offline operations,

plus…plus… New ALTER INDEX…REBUILD:New ALTER INDEX…REBUILD:

ONLINE – allows concurrent user access (queries as ONLINE – allows concurrent user access (queries as well as modifications) to the index during rebuildwell as modifications) to the index during rebuild

OFFLINE – works using locks (same as SQL Server™ OFFLINE – works using locks (same as SQL Server™ 2000)2000)

If online is not possible by default, consider If online is not possible by default, consider design alternatives to fully leverage online design alternatives to fully leverage online index rebuildsindex rebuilds

Online Index RebuildsOnline Index Rebuilds


Readers and Writers desire the same dataReaders and Writers desire the same data In SQL Server™ 2000In SQL Server™ 2000

Locking Locking is used to guarantee the intended level of is used to guarantee the intended level of isolationisolation

Users must wait to access locked dataUsers must wait to access locked data Concurrency and performance compromisedConcurrency and performance compromised Correctness is compromised when lower isolation Correctness is compromised when lower isolation

levels are used to avoid lockinglevels are used to avoid locking

In SQL Server™ 2005In SQL Server™ 2005 Locking Locking OR OR Versioning Versioning can be used to guarantee a can be used to guarantee a

variety of isolation levelsvariety of isolation levels With With versioningversioning, Readers won’t block writers and , Readers won’t block writers and

writers won’t block readerswriters won’t block readers Performance improved if contention was primary Performance improved if contention was primary

bottleneckbottleneck Correctness is not compromised due to use of lower Correctness is not compromised due to use of lower

isolation levelsisolation levels

Snapshot IsolationSnapshot IsolationImproving Concurrency in Mixed Improving Concurrency in Mixed WorkloadsWorkloads SQL Server™ 2000SQL Server™ 2000

Isolation implemented solely through lockingIsolation implemented solely through locking Mixed workloads may experience:Mixed workloads may experience:

Concurrency problems due to blockingConcurrency problems due to blocking The Inconsistent Analysis problemThe Inconsistent Analysis problem

SQL Server™ 2005SQL Server™ 2005 Isolation implemented using locking and Isolation implemented using locking and

versioningversioning Mixed workloads can improve read consistency Mixed workloads can improve read consistency

and performance using:and performance using: Read committed with Statement-level snapshot to Read committed with Statement-level snapshot to

improve statement-level consistencyimprove statement-level consistency Snapshot Isolation to improve transaction-level Snapshot Isolation to improve transaction-level

consistencyconsistency

Snapshot IsolationSnapshot Isolation



Data Access Concurrency LimitationsData Access Concurrency Limitations User or Application ErrorUser or Application Error Database Server Failure or DisasterDatabase Server Failure or Disaster

Failover ClusteringFailover Clustering Database MirroringDatabase Mirroring Peer-to-Peer ReplicationPeer-to-Peer Replication Log ShippingLog Shipping

Database MirroringDatabase MirroringDatabase-level RedundancyDatabase-level Redundancy

Upcoming High Availability Upcoming High Availability TechnologyTechnology

Released for testing and prototyping Released for testing and prototyping in SQL Server™ 2005 RTMin SQL Server™ 2005 RTM

Certified for Production Use in the Certified for Production Use in the first half of 2006first half of 2006

Supports three configurations:Supports three configurations: High AvailabilityHigh Availability High ProtectionHigh Protection High PerformanceHigh Performance

Commit

Write to

Local Log

Transmit to Mirror

Write to Remote

Log

Acknowledge

Committed in Log

Constantly Redoing on Mirror

Acknowledge

Database MirroringDatabase Mirroring

Log DBDB Log

Database MirroringDatabase MirroringConfiguration SummaryConfiguration Summary

No Automatic No Automatic DetectionDetection

Manual FailoverManual Failover Uses synchronous Uses synchronous

form of mirroringform of mirroring Does not require Does not require

WitnessWitness Principal Principal

performance is performance is affected by affected by network speed network speed and distanceand distance

High Availability

High Protection High Performance

Automatic Automatic DetectionDetection

Automatic Automatic FailoverFailover

Uses Uses synchronous synchronous form of form of mirroringmirroring

Requires Requires WitnessWitness

Principal Principal performance is performance is affected by affected by network speed network speed and distanceand distance

No Automatic No Automatic DetectionDetection

Manual FailoverManual Failover Uses Uses

asynchronous asynchronous form of mirroringform of mirroring

Does not require Does not require WitnessWitness

Principal Principal performance is performance is NOT affected by NOT affected by network speed network speed and distanceand distance

Database MirroringDatabase Mirroring

Which Technology When?Which Technology When?

Downtime – Time to Detect, Failover/Recover and Resume WorkloadDowntime – Time to Detect, Failover/Recover and Resume Workloads e c o n d ss e c o n d s to to m i n u t e sm i n u t e s to to h o u r sh o u r s to to d a y sd a y s

Failover Failover ClusteringClusteringFailover Failover

ClusteringClustering

Database Database MirroringMirroring

High Availability Configuration


High Availability Configuration

Work

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Failover Failover ClusteringClusteringGeographically

Dispersed

Failover Failover ClusteringClusteringGeographically

Dispersed


High Performance Configuration


High Performance Configuration ReplicationReplicationPeer-to-Peer Transactional

ReplicationReplicationPeer-to-Peer Transactional

Log Shipping Log Shipping Log Shipping Log Shipping

Backup/RestoreBackup/RestoreOnline Page-level to File-level to Filegroup-level to

Offline Database

Backup/RestoreBackup/RestoreOnline Page-level to File-level to Filegroup-level to

Offline Database

Detach/AttachDetach/AttachDetach/AttachDetach/AttachDatabase Database SnapshotSnapshotDatabase Database SnapshotSnapshot

Summary: Standby Summary: Standby TechnologiesTechnologiesTechnologyTechnology StandbyStandby ProtectionProtection WhenWhen

Failover ClusteringFailover Clustering HotHot ServerServer Minimal Work Minimal Work to Leverageto Leverage

Database MirroringDatabase MirroringHigh Availability ConfigurationHigh Availability Configuration HotHot DatabaseDatabase Minimal Work Minimal Work

to Leverageto Leverage

Log ShippingLog Shipping WarmWarm DatabaseDatabase Minimal Work Minimal Work to Leverageto Leverage

Database MirroringDatabase MirroringHigh Protection ConfigurationHigh Protection Configuration WarmWarm DatabaseDatabase Minimal Work Minimal Work


Database MirroringDatabase MirroringHigh Performance ConfigurationHigh Performance Configuration WarmWarm DatabaseDatabase Minimal Work Minimal Work


ReplicationReplication WarmWarmDatabaseDatabase(Publication of (Publication of

objects)objects)

Design and Design and ArchitectArchitect

Partial Database Partial Database AvailabilityAvailability OnlineOnline Filegroup/FileFilegroup/File Upgrade Upgrade

ImmediateImmediate

Backup and RestoreBackup and Restore ColdCold DatabaseDatabaseFilegroup/FileFilegroup/File


Barriers To AvailabilityBarriers To AvailabilityHow SQL Server 2005 Addresses How SQL Server 2005 Addresses ThemThem Database Maintenance and OperationsDatabase Maintenance and Operations

Fast RecoveryFast Recovery Partial AvailabilityPartial Availability Online RestoreOnline Restore Media ReliabilityMedia Reliability Dedicated Administration ConnectionDedicated Administration Connection Dynamic ConfigurationDynamic Configuration

Data Access Concurrency LimitationsData Access Concurrency Limitations Snapshot IsolationSnapshot Isolation Online Index OperationsOnline Index Operations ReplicationReplication Data PartitioningData Partitioning

Database Server Failure or DisasterDatabase Server Failure or Disaster Failover ClusteringFailover Clustering Database MirroringDatabase Mirroring Peer-to-Peer ReplicationPeer-to-Peer Replication Log ShippingLog Shipping

Building Highly Available Systems with SQL Server™ 2005 Vineet Gupta Evangelist – Data and...

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