Overview Of Replication
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This chapter provides you with an overview of how Replication replicates data.
How Replication Replicates Data
This section introduces the processes that Replication uses to replicate data. Before you can replicate data, you must define Replication. For more information on how to define replication, see Chapter 6. “Administering and Monitoring Replication.” Replication mainly uses three major processes to replicate data.
- Catch transactions
- Circulate data for replication
- Apply replicated data
Catch Transactions
CSQL Replication uses a log-based transaction-capture mechanism to capture committed transactions. A log-based transaction capture minimizes the effect on transaction performance.
Circulate Data for Replication
CSQL Replication uses the message queue to ensure that all the logs reach the appropriate server, regardless of a network or system failure. In the event of a failure, the message queue stores the logs until the network or system is operational. The message queue replicates data efficiently with a minimum of data copying and data transfer.
Apply Replicated Data
CSQL Replication uses a data-synchronization process to apply the replicated data to destination site. The destination database servers acknowledge receipt of a message when the message is safely stored. If the destination site fails to apply the log sent by the source then it could be because of connection failure or execution failure.
If it is the connection failure then the logs are sent after connection is reestablished, if it is execution failure then the entire transaction is written into the conflict resolution file.
Thus, this process ensures that transactions are applied at the destination site in the same order, as they were committed on the source database server.
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