Streaming Replication

Currently, MariaDB begins the replication process only after a transaction has commit (excluding 2-phase XA transactions). This can lead to greatly increased slave lag for workloads that have large transactions due to commit-ordering constraints. That is, a large transaction will block all future transactions from committing until it has commit.

This ticket is to implement a new mode of replication that would allow transactions to begin replication before commit time. That is, chunks of a transaction would be sent to a slave for "optimistic" replication (not in the sense of slave_parallel_mode) in real time, and then once the transaction has commit/rolled back on the master, the master would then send the commit to the slave. Note that a GTID would only be assigned at commit-time; partial transaction data that is sent to the slave could not have a GTID assigned.