QAD数据库双机热备

The target database

The target database is an identical copy of the source database. A second target database can be set up for additional redundancy. The target database:

Originates from the source database and contains the same data, schema, logical structure, and some of the same startup arguments as the source database.

Is updated solely by the OpenEdge Replication agent.

Does not allow database updates by anything other than OpenEdge Replication.

Permits queries and reports by users, as well as any non-database write activity (database utilities, for example) if OpenEdge Replication Plus is installed. For information on what

your OpenEdge Replication installation supports, see the “Database access once

OpenEdge Replication is running” section on page 3–23. See the “Utilities and OpenEdge Replication” section on page 5–51 for supported non-database write activity.

复制模式

OpenEdge Replication failure processing

If a failure does occur, such as a lost TCP/IP connection between the OpenEdge Replication server and the OpenEdge Replication agent, failure processing starts. If a failure occurs on the OpenEdge Replication server, it starts a process known as failure recovery. If a failure occurs on the OpenEdge Replication agent, the agent prepares to perform transition, which takes place if the connection to the server remains lost. For OpenEdge Replication to continue normal operations after a failure and after re-establishing a connection, the OpenEdge Replication server and the OpenEdge Replication agent must perform synchronization.

The sections that follow describe synchronization, server failure recovery, and agent failure recovery, including transition.

Synchronization

Synchronization is the process performed by the OpenEdge Replication server and the OpenEdge Replication agent to ensure that the source database and target database are identical. Synchronization is performed during database and replication startup and during failure

recovery processing.

Server failure recovery

Failure recovery is the process that the OpenEdge Replication server performs after a communication failure with the OpenEdge Replication agent. During failure recovery, the OpenEdge Replication server attempts to reconnect to an OpenEdge Replication agent or agents that have lost connection with the OpenEdge Replication server. After connection is

re-established, the OpenEdge Replication server and OpenEdge Replication agent attempt to synchronize. Once synchronization is complete, normal operations resume.

If the failure recovery operation is unsuccessful, the OpenEdge Replication server removes the failed agent from its list of OpenEdge Replication agents. If all OpenEdge Replication agents

fail and connection cannot be established, the OpenEdge Replication server stops. If the server stops, source databases activities continue and AI extents continue to fill.

Agent failure recovery

Transition is the action that the OpenEdge Replication agent performs after a communication failure has occurred with the OpenEdge Replication server. Within the transition-timeout

value (as defined in source-db-name.repl.properties, the OpenEdge Replication server

properties file), the OpenEdge Replication agent listens for connection requests from the OpenEdge Replication server. After connection is established, the OpenEdge Replication server and OpenEdge Replication agent perform synchronization. Once synchronization is complete, normal operations resume.

If the OpenEdge Replication agent does not receive a communication attempt within a set length of time (the transition-timeout value), and auto-transition has been configured, the target

database is transitioned into a normal OpenEdge database. If manual transition has been configured, the OpenEdge Replication agent continues to wait for connection until either

manual transition is performed using the DSRUTIL utility or the database is shut down. For

more information about the DSRUTIL utility, see the “DSRUTIL utility” section on page 5–11.

Enhanced Read-Only mode

When the OpenEdge Replication agent is running, the database is placed into an Enhanced

Read-Only mode (ERO).

如果，目标数据库断开连接，源数据库将进入延迟等待，每5分钟尝试连接一次，进行同步