3 ms·

What is interesting is that a lot of hard problems can be solved by making the network more reliable. For example here is the writeup by Eric Brewer (of CAP fa

What is interesting is that a lot of hard problems can be solved by making the network more reliable. For example here is the writeup by Eric Brewer (of CAP fame) how Google is able to achieve CA (consistency and availability) in practice because of their reliable network architecture. https://cloud.google.com/blog/products/databases/inside-cloud-spanner-and-the-cap-theorem https://cloud.google.com/blog/products/databases/inside-clou... Along the same lines, notice that while the first message can be arbitrarily long (for example the time and date of the attack, maybe the strategy), the ACK is only a single bit. So in practice, Alice's message could be, "Attack on May 9th at Dawn, and as soon as you receive the message, set the hill behind you on fire." So no matter how good the enemy is at capturing messengers, if at least one messenger gets through, and Alice is able to notice whether the hill behind Bob is on fire, they will be able to coordinate successfully.

hangonhn 4y ago
Michael Stonebaker made a very similar argument as well: https://cacm.acm.org/blogs/blog-cacm/83396-errors-in-database-systems-eventual-consistency-and-the-cap-theorem/fulltext https://cacm.acm.org/blogs/blog-cacm/83396-errors-in-databas... Quote: "Let us now turn to cases where the CAP theorem might apply. Consider error 6 where a LAN partitions. In my experience, this is exceedingly rare, especially if one replicates the LAN (as Tandem did). Considering local failures (3, 4, 5, and 6), the overwhelming majority cause a single node to fail, which is a degenerate case of a network partition that is easily survived by lots of algorithms. Hence, in my opinion, one is much better off giving up P rather than sacrificing C. (In a LAN environment, I think one should choose CA rather than AP). Newer SQL OLTP systems (e.g., VoltDB and NimbusDB) appear to do exactly this."
anamax 4y ago
However, "Alice is able to notice" isn't a given. Yes, setting a hill on fire may be more likely to "get through" than sending a messenger in response, but there's still a chance that the fire won't be seen. And, if no messengers (from Alice) got through, you might decide to set the hill on fire anyway, not knowing how Alice will interpret that act. Yes, better networks help, but as long as they're short of perfect....
immigrantheart 4y ago
What if you need to serve 3rd world countries? Unreliable internet connection is the norm. A company with Google scale would encounter something like that.
foft 4y ago
Say the enemy captures the messenger and sets the hill on fire? Bob never receives the message so Alice attacks alone.

hangonhn 4y ago

Michael Stonebaker made a very similar argument as well: https://cacm.acm.org/blogs/blog-cacm/83396-errors-in-database-systems-eventual-consistency-and-the-cap-theorem/fulltext https://cacm.acm.org/blogs/blog-cacm/83396-errors-in-databas... Quote: "Let us now turn to cases where the CAP theorem might apply. Consider error 6 where a LAN partitions. In my experience, this is exceedingly rare, especially if one replicates the LAN (as Tandem did). Considering local failures (3, 4, 5, and 6), the overwhelming majority cause a single node to fail, which is a degenerate case of a network partition that is easily survived by lots of algorithms. Hence, in my opinion, one is much better off giving up P rather than sacrificing C. (In a LAN environment, I think one should choose CA rather than AP). Newer SQL OLTP systems (e.g., VoltDB and NimbusDB) appear to do exactly this."

anamax 4y ago

However, "Alice is able to notice" isn't a given. Yes, setting a hill on fire may be more likely to "get through" than sending a messenger in response, but there's still a chance that the fire won't be seen. And, if no messengers (from Alice) got through, you might decide to set the hill on fire anyway, not knowing how Alice will interpret that act. Yes, better networks help, but as long as they're short of perfect....

immigrantheart 4y ago

What if you need to serve 3rd world countries? Unreliable internet connection is the norm. A company with Google scale would encounter something like that.

foft 4y ago

Say the enemy captures the messenger and sets the hill on fire? Bob never receives the message so Alice attacks alone.