If you make frequent updates, yet require very up-to-date information, you will need to set a short propagation interval, to simulate real-time replication. If you want to minimize your communication costs, you may prefer to increase this interval to once a day, or even once a week.
If you require information that is up to date as of a particular point in time, you may prefer to propagate your changes at a scheduled time. For example, you might want to retrieve new pricing information at the start of each quarter.
Finally, if you do not know when your network connection will be available, such as if you are using a laptop computer to collect data on a sales call, you may want to propagate your changes on demand.
Because snapshot sites propagate changes only to their associated master site, and because they pull down changes from their master in an efficient, batch-oriented manner, sites requiring on-demand data propagation should typically be snapshot sites.
In addition to determining an appropriate replication interval for each site, you must also determine what data is appropriate for each site.
Certain sites may not require full copies of a replication group, and you may prefer to replicate only a subset of the data to these sites to conserve resources. For example, suppose you have regional branches of your business, each with their own client base. Each branch may require full copies of certain tables, such as price lists, but only subsets of others, such as customer lists. Because master sites must contain full copies of a replicated group, these branch sites would need to be created as snapshot sites.
The following sections of this chapter describe the various models that Oracle's symmetric replication facility supports in more detail, including hybrid models that combine snapshot and multi-master replication.