3 ms·

Nope, this is in fact synchronous. It just degrades gracefully when one of the disaster domains is impacted. The main purpose here AIUI is availability, rather

Nope, this is in fact synchronous. It just degrades gracefully when one of the disaster domains is impacted. The main purpose here AIUI is availability, rather than durability. For durability, you'll indeed want something like 3-way replication. But that's a distinct problem. If durability is your concern but you're fine with the availability SLOs of a single disaster domain, then you don't need regional replication.

foota 2y ago
Is the idea that you'll check replication status after making each write? Or I guess you could do this at the application level, like after completing a transaction to e.g., sqlite check that there's at least one other zone caught up before acking whatever call the user made?
- leg 2y ago
  Many enterprise storage systems have the durability/availability tradeoff like these replicated disks when replicating outside of a single datacenter. (Oracle calls it "max availability": try to synchronously replicate, but if the remote side is offline, allow transactions to commit.) Real world banks run on these sorts of systems. Users don't continuously check replication status. They rely on it being synchronous almost all the time. 3 way quorum replication is great, but you then need to send to more data centers, potentially affecting performance. There's a tradeoff. (I work on GCP storage)
gregwebs 2y ago
It’s synchronous much of the time but can become asynchronous at any moment? I would still call that asynchronous. The availability story isn’t incredible either. Once the secondary is behind an outage of the primary means the system is no longer operational until that primary can be restored. Three-way replication with raft and 2/3 or 3/5 acks is what modern distributed databases use. It’s for both availability and durability.

3 ms·

Nope, this is in fact synchronous. It just degrades gracefully when one of the disaster domains is impacted. The main purpose here AIUI is availability, rather

by Balinares 2y ago

foota 2y ago
Is the idea that you'll check replication status after making each write? Or I guess you could do this at the application level, like after completing a transaction to e.g., sqlite check that there's at least one other zone caught up before acking whatever call the user made?
- leg 2y ago
  Many enterprise storage systems have the durability/availability tradeoff like these replicated disks when replicating outside of a single datacenter. (Oracle calls it "max availability": try to synchronously replicate, but if the remote side is offline, allow transactions to commit.) Real world banks run on these sorts of systems. Users don't continuously check replication status. They rely on it being synchronous almost all the time. 3 way quorum replication is great, but you then need to send to more data centers, potentially affecting performance. There's a tradeoff. (I work on GCP storage)
gregwebs 2y ago
It’s synchronous much of the time but can become asynchronous at any moment? I would still call that asynchronous. The availability story isn’t incredible either. Once the secondary is behind an outage of the primary means the system is no longer operational until that primary can be restored. Three-way replication with raft and 2/3 or 3/5 acks is what modern distributed databases use. It’s for both availability and durability.