7 ms·
MTBF of 2PC-strapped-to-quorum is no different from MTBF of a 2PC-strapped-to-spof replicas. MTTR is bounded by reelection latency, rather than replica recover
by krenoten 10y ago
MTBF of 2PC-strapped-to-quorum is no different from MTBF of a 2PC-strapped-to-spof replicas.
MTTR is bounded by reelection latency, rather than replica recovery, although you still may eat a write amplification cost for rereplication.
write amplification is 3-5x of non-quorum-backed 2PC system, depending on replication ensemble size.
google further multiplies write amplification with geo-redundancy, so bump that WA by another 3x+.
it's an insanely high cost to pay for availability, but for an advertising company it's important to count the beans accurately.
- jasonwatkinspdx 10y agoYou're making some assumptions. For example if you use epaxos for the quorums there is no unavailability due to a leader failure and re-election. Even then, re-election is likely going to be a lot faster than any sort of fault tolerant 2PC coordinator recovery protocol. You're exaggerating the write amplification. The above offering is single region. Google says they do 5 way geo in their various papers/etc, and there's no way they're paying some cumulative 15 copy write amplification as you imply.
- krenoten 10y agoepaxos is not general purpose replication. It leaves the problem of reconciling multiple replication streams to another layer. I've heard that they do 20+WA (distributed, before you consider on-disk WA) for much of it. shrug
- findateamfirst 10y agoI've worked on a storage system that used 9. 15 doesn't seem impossible to me.
- ec109685 10y ago9x write amplification isn't that high. If you are setup with a master slave configuration, that creates write amplification and for reliability, you probably have some sort of raid, that increase the number of places writes go to as well.
- inopinatus 10y agoNot necessarily RAID, it might be an erasure coding.