A 3-node Raft group has its leader in US East and followers in US West (70 ms round trip from the leader) and Europe (80 ms). About how long does the leader take to commit a write?

Answer

About 70 ms. In review, anything from 46.7 to 105 counts as right.

The worked estimate

A commit needs a majority, 2 of 3: the leader itself plus the first follower to store the entry. That is one round trip to the nearest follower, about 70 ms, plus disk writes. The slower European follower does not delay commits, but if US West fails, every write waits 80 ms.

Numbers: Numbers to know.

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