Right now synchronous replication in postgresql chooses one replica as synchronous and waits for replies from it (with synchronous_commit = on | remote_write) until this replica host does not disconnect from master.
Are there any plans to implement something like semi synchronous replication in MySQL 5.6 or replication with write_concern=2 in MongoDB when the master waits for a reply from any of the replica hosts?
When the sync replica dies or the network between master and sync replica flaps, 3 seconds must pass before the potential replica becomes sync and transaction commits continue. Instead postgresql could wait for confirm from first or second replica hosts (doesn’t matter which of them answers first), couldn’t it? In this case transaction commits will not stuck for wal_sender_timeout.
In this case network flaps between master and any one replica will not affect writing load and in case of master fail it would be necessary to find the most recent replica and promote it. Or there are pitfalls that I do not see?
