Jeff Garzik wrote: > Jamie Lokier wrote: > >Look up "one-phase commit" or even "zero-phase commit". (The > >terminology is cheating a bit.) As I've understood it, all commit > >protocols have a step where each node guarantees it can commit if > >asked and node failure at that point does not invalidate the guarantee > >if the node recovers (if it can't maintain the guarantee, the node > >doesn't recover in a technical sense and a higher level protocol may > >reintegrate the node). One/zero-phase commit extends that to > >guaranteeing a certain amounts and types of data can be written before > >it knows what the data is, so write messages within that window are > >sufficient for global commits. Guarantees can be acquired > >asynchronously in advance of need, and can have time and other limits. > >These guarantees are no different in principle from the 1-bit > >guarantee offered by the "can you commit" phase of other commit > >protocols, so they aren't as weak as they seem. > > For several common Paxos usages, you can obtain consensus guarantees > well in advance of actually needing that guarantee, making the entire > process quite a bit more async and parallel. > > Sort of a "write ahead" for consensus. That's a lovely concise summary. It seems all the classical texts on two-phase commit have made it over-complicated all along. "write ahead consensus" is both faster and simpler in many respects. -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
