Configuring a cascaded replication
As you have already seen in this chapter, setting up streaming replication is really easy. All it takes is setting a handful of parameters, taking a base backup, and enjoying your replication setup.
In many cases, however, the situation is a bit more delicate. Let's assume for this example that we want to use a master to spread data to dozens of servers. The overhead of replication is actually very small (common wisdom says that the overhead of a slave is around 3 percent of overall performance—however, this is just a rough estimate), but if you do something small often enough, it can still be an issue.
It is definitely not very beneficial for the master to have, say, 100 slaves.
An additional use case is as follows: having a master in one location and a couple of slaves in some other location. It does not make sense to send a lot of data over a long distance over and over again. It is a lot better to send it once and dispatch it to the other...
