MySQL 26.7 Release Notes
MySQL provides the following implementations for applying transactions on a replica:
Applier version 1 is the existing Multi-Threaded Applier (MTA).
Applier version 2 is the Change Stream Applier (CSA), introduced in MySQL 26.7.0.
The applier implementation is selected separately for each
replication channel using the APPLIER_VERSION
option of CHANGE REPLICATION SOURCE TO. Version
1 is the default for a new channel.
The CSA uses a scheduler and a channel-specific pool of worker
sessions. It determines transaction dependencies from the
last_committed and
sequence_number values recorded in GTID events.
Transactions whose dependencies are satisfied can be applied in
parallel.
If replica_preserve_commit_order
is enabled, the apply and commit phases are scheduled separately.
A transaction that has finished applying waits for its turn to
register for commit, but the worker that applied it can process
another ready transaction instead of waiting. The commit order
manager preserves the order in which transactions were committed
on the source.
CSA workers can read transaction events from the relay log in parallel and release event memory as events are consumed. Relay log files can be marked for purging concurrently when they have been completely read and all transactions that use them have been applied successfully.