Asynchronous Update Propagation
Collect updates at primary using triggers or the log
Triggers (Oracle, Rdb, SQL Server, DB2, …)
- On every update at the primary, a trigger fires to store the update in the update propagation table.
Post-process (“sniff”) the log to generate update propagations (SQL Server, DB2, Tandem Non-Stop SQL)
- Off-line, so saves trigger and triggered update overhead, though R/W log synchronization also has a cost
- Requires admin (what if the log sniffer fails?)
Optionally identify updated fields to compress log
Most DB systems support this today.
- First in IBM IMS, Tandem NS SQL, DEC/Rdb, & ad hoc