In PostgreSQL, there are two kinds of replication techniques:
- Asynchronous replication: In asynchronous replication, the primary device (source) sends a continuous flow of data to the secondary one (target), without receiving any return code from the target. This type of copying has the advantage of speed, but it brings with it greater risks of data loss because the received data is not checked.
- Synchronous replication: In synchronous replication, a source sends the data to a target, that is, the second server; at this point, the server sends back a code to verify the correctness of the data. If the check is successful, the transfer is completed.
Both methods have advantages and disadvantages, and in the Managing streaming replication section of this chapter, we will analyze them.
WAL
Let's briefly summarize what we saw in the chapter on MVCC and WAL: in that chapter, we saw how PostgreSQL stores data on disk using WAL; as we saw in Chapter 11, Transactions...
