Patroni: synchronous_mode vs maximum_lag_on_failover

Question

Here is documentation of Patroni https://patroni.readthedocs.io/en/latest/replication_modes.html.

There are two options: maximum_lag_on_failover and synchronous_mode.

In the project, I see these two options are set (synchronous_mode: true, maximum_lag_on_failover: 1048576 ). Does it make sense?

One says you can promote secondary to primary with a lag of 1048576 bytes, and second, says you can't promote secondary to primary if you have any lag. And the second question does maximum_lag_on_failover works only on async replication, and synchronous_mode only on sync replication?

Answer 1

I do not have enough reputation to post it as a comment, but, I suppose that maximum_lag_on_failover still could be used with synchronous_mode: true, because as it is said in docs: Turning on synchronous_mode does not guarantee multi node durability of commits under all circumstances. When no suitable standby is available, primary server will still accept writes, but does not guarantee their replication. . So, in order to provide availability patroni in synchronous_mode stil allowed to lose some transactions. Also If I recall correctly, in our project we had both options set and everything worked normally. The other question is: Is it possible to use maximum_lag_on_failover together with synchronous_mode_strict: true