How Multi-site Systems Work

Each distributed system in a multi-site configuration operates independently of the other connected systems. Each system can be configured as necessary for the resources available at the local site, as well as the local topology (peer-to-peer and/or client-server).

However, tables that are configured for replication between sites must be created using identical table names and column definitions. In addition, gateway senders and receivers must be configured to assign logical gateway connections to physical network connections in each system.

For each table that is configured to use a gateway sender, DML events are automatically forwarded to the gateway sender for distribution to other sites. The events are placed in a gateway queue and distributed asynchronously to remote sites. The ordering of events sent between sites is preserved. The following types of DML operations are distributed:
  • inserts
  • updates
  • deletes (except for data deletion associated with table expiration).
Other operations are not distributed, such as:
  • Queries against the table
  • DDL operations of any kind
  • Expiration actions of any kind
  • Transaction boundaries that involve the configured table

If the queue of DML events becomes too full, it is overflowed to a disk store to keep the member from running out of memory. Optionally, you can configure the queue to be persisted to disk. With persistence, if the member that manages the queue goes down, the member picks up where it left off after it is restarted.