maria-developers team mailing list archive
Mailing list archive
Re: [Commits] Rev 4376: MDEV-6676: Speculative parallel replication in http://bazaar.launchpad.net/~maria-captains/maria/10.0
Robert Hodges <robert.hodges@xxxxxxxxxxxxxx> writes:
> There is one thing I have never understood about your parallel apply
> algorithm. How do you handle the case where the server crashes when some
> threads have committed but others have not? It seems as if you could have
> a problem with recovery.
Transactions are executed in parallel, but they are committed sequentially.
So if we crash, there is always a single point before which all transactions
are committed and after which no transactions are.
If using InnoDB and global transaction ID, this point is saved in a crash-safe
way, so no problems with crash recovery.
If using MyISAM, or if using old filename/offset position in relay-log.info,
then a crash may leave an inconsistency - but this is also the case with
A substantial effort was spent in the code to make the sequential commit of
the parallelly applied transaction efficient. For example, it is possible for
such transactions to be group committed.