this was on about 33rd minute of the presentation
He suggested , that if you need to use , synchronous replication, to use PostgreSQL 10 with synchronous quorum replication, so that it will not block transactions if one of the replicas fail.
It is a tradeoff though. With synch rep, you are at a minimum adding the cost of two network trips to the latency of each write (distributed consistent databases like Cassandra pay this cost as well, which is why they tend to have relatively high write latency). It turns out that a lot of users are willing to lose a few transactions in a combination failure case instead of having each write take three times as long.
Postgres also has some "in between" modes because write transactions can be individually marked as synch or asynch, so less critical writes can be faster. I believe that Cassandra has something similar.