The IBM InfoSphere Change Data Capture (IBM Infosphere CDC) components are responsible for carrying the data between the backend database and the cache database – both ways.

Replication with IBM InfoSphere Change Data Capture can take the form of one time snapshot (refresh) of cached data or continuous update propagation between the systems. The continuous replication method is asynchronous in nature: the data is first committed on the local system (the source) and then propagated to the other system (the target). The delay is usually within a second.

IBM Infosphere CDC uses log-scraping technologies, triggers, or both to capture databases changes. The cache replication engine accesses the solidDB^® transaction log to capture data changes and transmits these changes to the backend replication engine, which copies the changes to the backend database. Similarly, the backend replication engine accesses the log (or uses triggers) to capture data changes in the backend database and transmits these changes to the cache replication engine, which copies the changes to the cache database.

Asynchronous replication method means that as applications write, for example, to the cache database, control is returned to the application as soon as the write completes; the application does not block, waiting for these updates to be successfully applied to the backend. Updates to the backend are not performed until the following tasks are completed:

In the Universal Cache system, asynchronous replication benefits applications by reducing the round-trip time required to access data. Instead of potentially incurring an expensive network hop and writing to the backend database, applications can write directly to the solidDB^® database. Asynchronous replication means also that applications cannot assume that the backend database has been written to at the same time as the cache database, which can have ramifications for error recovery.