Data currency reflects how up to date you want the copy tables to be. IBM Replication makes it very easy to control the Apply program processing interval and therefore the currency of the data. It is sometimes very tempting to start out wanting your copies to be as current as possible. In a test environment, you might be setting all frequency intervals to the minimum. When moving to production, it is advisable to start with a mid-range frequency value and "tune" your system from that point.
Although customers have devised many creative ways of controlling the replication subscription timing mechanism, the most typical ways are:
This is the normal mode of operation. In general, replication subscriptions work on a subscription-level interval basis; that is, you specify a refresh interval to be continuous or between 1 minute and 1 year for the replication subscription and all of its members. The interval can be set and changed by using the Control Center or, standard SQL against the subscription set control table.
The copy operation can be carried out as a result of an application or user action. This can be done by specifying an event name when you define the subscription in the Control Center, and then populating the subscription event control table with the event name when it is time to trigger the replication subscription. Event-based timing can be used together with interval timing for the same subscription.
You define subscription timing with the Subscription Timing notebook from the Control Center, and control the timing using time-based and event-based scheduling. These timing options can be used together or independently of each other. For example, you can set an interval of one day, but specify that an event can also trigger the subscription cycle.
The simplest method is to use the time-based frequency and allows the subscription to be run at a set interval (relative timing) or continuously. The entire subscription set is replicated on the same frequency. Relative timing allows you to specify an interval in minutes, hours, days, or weeks at which the subscription set is replicated.
Choosing a relative timing interval does not guarantee that the frequency will be exactly at that interval. When you decide on the refresh interval for the replication subscription, you should determine whether it is possible to refresh all tables in the replication subscription within the given interval. To check this, determine the amount of data that the Apply program is likely to select for each interval and estimate the time that it will take to copy the data.
Continuous timing allows you to have the subscription set replicated as frequently as the Apply program can replicate the data.
Setting an event-based frequency allows you to use an event to trigger replication of the replication subscription by the Apply program. You supply an event name while defining the replication subscription with the Control Center and then have an application or a user populate the subscription event control table with the event value. When the Apply program detects the event value, it begins the process of replicating the replication subscription. The Control Center does not manage the triggering of the Apply program. You are responsible for populating the event table.