1. Replication Guide
  2. Defining an Active Standby Pair Replication Scheme
  3. Restrictions on Active Standby Pairs

Restrictions on Active Standby Pairs

Keep in mind the restrictions when you are planning an active standby pair replication scheme.

  • To ensure high availability, each active and standby master databases as well as all subscriber databases should be on different machines.

  • The Linux or UNIX platforms for each host on which the master databases reside should have the same operating system kernel settings for shared memory and semaphores.

  • For best replication performance a fast, stable network is best. The following can stall or impede replication progress.

    • Slow network: A slow network directly affects transaction rate of replication. Enabling compression could help. See Store Data Efficiently With Column-Based Compression of Tables in the Oracle TimesTen In-Memory Database Operations Guide.

    • Network outage: In the event of a network outage, replication operations stop and only resume when a connection is active between sender and receiver.

  • The active and standby masters must have their clocks synchronized through NTP or other means. The clock skew between the active master and the standby master cannot exceed 250 milliseconds. When adjusting the system clocks on any nodes to be synchronized with each other, do not set any clock backward in time.

  • For the initial setup, you create the standby database by duplicating the active database with the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function.

  • ALTER ACTIVE STANDBY PAIR statements can run only on the active database. If ALTER ACTIVE STANDBY PAIR is run on the active database, then the standby database must be regenerated by duplicating the active database. All subscribers must also be regenerated from the standby database. See Duplicating a Database.

  • Read-only subscribers can be created only by duplicating the standby database. If the standby database is unavailable, then the read-only subscribers can be created by duplicating the active database. See Duplicating a Database.

  • You can specify up to 254 subscribers,

  • Replication from the standby database to the read-only subscribers occurs asynchronously.

  • Write operations on replicated tables are not allowed on the standby database or the subscriber databases. However, operations on sequences and XLA bookmarks are allowed on the standby database and the subscriber databases. Read operations are also allowed.

  • After failover, the new standby database can only be recovered from the active database by duplicating the active database unless return twosafe replication is used between the active and the standby databases. If return twosafe replication is used, the automated master catch-up feature may be used instead. See Automatic Catch-Up of a Failed Master Database.

  • You cannot replicate a temporary database.

  • You cannot replicate tables with compressed columns.