Before we start replicating our first database, we have to dive into Slony's architecture. It is important to understand how it works, otherwise it will be next to impossible to utilize this software in a useful and reasonable way.

In contrast to transaction log streaming, Slony uses logical replication. This means that it does not use internal binary data (such as the XLOG) but a logical representation of the data (in the case of Slony, it is text). Using textual data instead of the built-in transaction log has some advantages, but also some downsides, which will be discussed in detail in this chapter.