After that introduction to synchronous replication and dynamically adjustable durability, I want to focus your attention on a feature called the replication slot.
What is the purpose of a replication slot? Let us consider the following example: there is a master and a slave. On the master, a large transaction is executed and the network connection is not fast enough to ship all the data in time. At some point, the master removes its transaction log (checkpoint). If the slave is too far behind, a re-sync is needed. As you have already seen, the wal_keep_segments setting can be used to reduce the risk of failing replication. The question is this: what is the best value for the wal_keep_segments setting? Sure, more is better, but how much is best?
Replication slots will solve this problem for you: if you are using a replication slot, a master can only...