Abstract: Database replication systems replicate blocks of transaction steps or operations with synchronous replication, and perform dual writes with queuing and blocking of transactions. Tokens are used to prepare a target database for replication from a source database and to confirm the preparation. Database replication systems switch between a synchronous replication mode and an asynchronous replication mode, and then back to a synchronous replication mode, based on detection of selected events.

Abstract: Transaction ping-pong is selectively prevented in a bidirectional database replication system. The system has a plurality of nodes connected via communication media in a topology. Each node includes a database and a transaction transmitter or collector which sends transactions posted to the database to a database at one or more other nodes for replication in the databases of the one or more other nodes. All transactions to be posted to databases in remote nodes that were sent by a local node are detected, and the database at the local node is inhibited from posting selective transactions which were detected as being originally sent by the local node.