DB2 9.5高可用与数据恢复指南：2009年更新

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DB2高可用与数据恢复是IBM数据库管理系统(DB2)的重要组成部分，特别是针对版本9.5的Linux、UNIX和Windows平台。这份文档——《DB2 Version 9.5 for Linux, UNIX, and Windows Data Recovery and High Availability Guide and Reference》（更新日期为2009年4月，编号SC23-5848-02），提供了深入理解和实践DB2在高可用性和数据恢复方面的关键指导。高可用性（High Availability，HA）是确保数据库服务连续运行，即使在系统出现故障时也能快速恢复正常的关键特性。它通过冗余配置、故障转移和负载均衡等技术来实现。在DB2 9.5中，可能涉及的数据复制、集群管理、灾备策略以及监控工具的使用，以最小化停机时间和数据丢失风险。数据恢复则是针对数据库意外中断或损坏情况下的数据保护措施。该文档详细阐述了如何执行备份策略、故障后的恢复过程，以及如何使用各种恢复工具，如快照、事务日志管理和数据一致性检查，来恢复数据完整性。此外，文档还可能包含如何处理不同类型的错误、数据恢复的最佳实践，以及如何进行灾难恢复演练。在使用这些功能时，用户必须注意文档中提及的注意事项，包括但不限于阅读附录B中的通用信息，了解版权声明、支持协议以及产品保修。此外，用户可以通过IBM官方网站（www.ibm.com）或联系本地IBM代表进行在线订购或获取更多相关信息。在维护和优化DB2的高可用性和数据恢复性能时，这份指南和参考手册是不可或缺的资源，它能帮助DB2管理员提高系统的稳定性和可靠性，降低潜在的风险，确保业务连续性。因此，对于任何想要深入学习和实践DB2的用户来说，这是一个宝贵的参考资料。

Active logs are used during crash recovery to prevent a failure (system power or

application error) from leaving a database in an inconsistent state. Active logs are

located in the database log path directory.

Archive logging

Archive logging is used specifically for rollforward recovery. Archived logs are logs

that were active but are no longer required for crash recovery. Use the logarchmeth1

database configuration parameter to enable archive logging.

Taking online backups is only supported if the database is configured for archive

logging. During an online backup operation, all activities against the database are

logged. When an online backup image is restored, the logs must be rolled forward

at least to the point in time at which the backup operation completed. For this to

happen, the logs must have been archived and made available when the database

is restored. After an online backup is complete, the DB2 database manager forces

DB2 server

Database Log Path

Transaction

Active Log Files

Circular Logs

Active

Log File

Figure 1. Circular Logging

TIME

Units of work Units of work

update update

Logs are used between backups to track the changes to the databases.

BACKUP

database

n archived logs

1 active log

n archived logs

1 active log

Figure 2. Active and Archived Database Logs in Rollforward Recovery. There can be more than one active log in the

case of a long-running transaction.

6 Data Recovery and High Availability Guide and Reference

the currently active log to be closed, and as a result, it will be archived. This

ensures that your online backup has a complete set of archived logs available for

recovery.

The following database configuration parameters allow you to change where

archived logs are stored: The newlogpath parameter, and the logarchmeth1 and

logarchmeth2 parameters. Changing the newlogpath parameter also affects where

active logs are stored.

To determine which log extents in the database log path directory are archived logs,

check the value of the loghead database configuration parameter. This parameter

indicates the lowest numbered log that is active. Those logs with sequence

numbers less than loghead are archived logs and can be moved. You can check the

value of this parameter by using the Control Center; or, by using the command

line processor and the GET DATABASE CONFIGURATION command to view the

″First active log file″. For more information about this configuration parameter, see

the Performance Guide book.

Log control files

When a database restarts after a failure, the database manager applies transaction

information stored in log files to return the database to a consistent state. To

determine which records from the log files need to be applied to the database, the

database manager uses information recorded in a log control file.

Redundancy for database resilience

The database manager maintains two copies of the log control file,

SQLOGCTL.LFH.1 and SQLOGCTL.LFH.2, so that if one copy is damaged, the

database manager can still use the other copy.

Performance considerations

Applying the transaction information contained in the log control files contributes

to the overhead of restarting a database after a failure. You can configure the

frequency at which the database manager writes transaction to disk in order to

reduce the number of log records that need to be processed during crash recovery

using the “softmax - Recovery range and soft checkpoint interval configuration

parameter” in Data Servers, Databases, and Database Objects Guide.

Chapter 1. High availability strategies 7

Chapter 2. High availability with IBM Data Server

IBM Data Server contains functionality that supports many high availability

strategies.

Automatic client reroute roadmap

Automatic client reroute is an IBM Data Server feature that redirects client

applications from a failed server to an alternate server so the applications can

continue their work with minimal interruption. Automatic client reroute can be

accomplished only if an alternate server has been specified prior to the failure.

Table 1 lists the relevant topics in each category.

Table 1. Roadmap to automatic client reroute information

Category Related topics

General information

v “Automatic client reroute limitations” on page 22

v “Automatic client reroute description and setup” on page 17

v “Automatic client reroute description and setup (DB2

Connect

™

)” in Quick Beginnings for DB2 Connect Servers

Configuration

v “Identifying an alternate server for automatic client reroute” on

page 21

v “Configuring automatic client reroute retry behavior using

registry variables” on page 19

v “Client reroute setup when using IBM Data Server Driver for

JDBC and SQLJ” on page 21

Examples

v “Automatic client reroute examples” on page 170

Interaction with other

DB2 features

v “Configuring automatic client reroute and High Availability

Disaster Recovery (HADR)” on page 29

v “Using client connection timeout with automatic client reroute”

on page 20

v “IBM Data Server Driver for JDBC and SQLJ client reroute

support” in Developing Java

™

Applications

Troubleshooting

v “Configuring automatic client reroute for client connection

distributor technology” on page 20

Note: Starting with Version 9.5 Fix Pack 3, automatic client reroute for DB2 for

z/OS

Sysplex is available in IBM data server clients and non-Java IBM data server

drivers. With this support, applications that access a DB2 for z/OS Sysplex can use

automatic client reroute capabilities provided by the client, and are not required to

go through a DB2 Connect server. For more information about this feature, see the

topic about automatic client reroute (client-side) in the DB2 Information Center.

DB2 fault monitor facilities for Linux and UNIX

Available on UNIX based systems only, DB2 fault monitor facilities keep DB2 Data

Server databases up and running by monitoring DB2 database manager instances,

and restarting any instance that exits prematurely.

The Fault Monitor Coordinator (FMC) is the process of the Fault Monitor Facility

that is started at the UNIX boot sequence. The init daemon starts the FMC and will

restart it if it terminates abnormally. The FMC starts one fault monitor for each

DB2 instance. Each fault monitor runs as a daemon process and has the same user

privileges as the DB2 instance.

Once a fault monitor is started, it will be monitored to make sure it does not exit

prematurely. If a fault monitor fails, it will be restarted by the FMC. Each fault

monitor will, in turn, be responsible for monitoring one DB2 instance. If the DB2

instance exits prematurely, the fault monitor will restart it. The fault monitor will

only become inactive if the db2stop command is issued. If a DB2 instance is shut

down in any other way, the fault monitor will start it up again.

DB2 fault monitor restrictions

If you are using a high availability clustering product such as HACMP

™

, MSCS, or

IBM Tivoli

System Automation for Multiplatforms, the fault monitor facility must

be turned off since the instance startup and shut down is controlled by the

clustering product.

Differences between the DB2 fault monitor and the DB2 health

monitor

The health monitor and the fault monitor are tools that work on a single database

instance. The health monitor uses health indicators to evaluate the health of specific

aspects of database manager performance or database performance. A health

indicator measures the health of some aspect of a specific class of database objects,

such as a table space. Health indicators can be evaluated against specific criteria to

determine the health of that class of database object. In addition, health indicators

can generate alerts to notify you when an indicator exceeds a threshold or

indicates a database object is in a non-normal state.

By comparison, the fault monitor is solely responsible for keeping the instance it is

monitoring up and running. If the DB2 instance it is monitoring terminates

unexpectedly, the fault monitor restarts the instance. The fault monitor is not

available on Windows.

High Availability Disaster Recovery (HADR)

The DB2 Data Server High Availability Disaster Recovery (HADR) feature is a

database replication feature that provides a high availability solution for both

partial and complete site failures. HADR protects against data loss by replicating

data changes from a source database, called the primary, to a target database,

called the standby.

HADR might be your best option if most or all of your database requires

protection, or if you perform DDL operations that must be automatically replicated

on the standby database.

Applications can only access the current primary database. Updates to the standby

database occur by rolling forward log data that is generated on the primary

database and shipped to the standby database.

A partial site failure can be caused by a hardware, network, or software ( DB2

database system or operating system) failure. Without HADR, a partial site failure

requires restarting the database management system (DBMS) server that contains

10 Data Recovery and High Availability Guide and Reference

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