Quorum

TODO: Quorum description

• При переполнении числа отказов система перестает отвечать, а не ведет себя произвольно
• Нет проблемы split brain

Reconfigurations

We need to add new replicas

• $2n \rightarrow 2n + 1$ is OK as majority does not change
• $2n + 1 \rightarrow 2n + 2$ is OK as quorums overlap

But we cannot add many replicas as quorums may not overlap!

Solution is ordering reconfigurations in replicated-log

• Commit C_1 in slot k, use config since slot k + a

Grid Quorum

Select row and column from grid