Stoppable Paxos
Summary
Stoppable state machines are used to implement reconfiguration, simply a reconfigurable state machine consists of several stoppable state machines. To switch between the configurations, one is stopped and the other is started.
Traditionally, reconfiguration is done by executing special reconfiguration commands as a consensus instance. However, it prevents the concurrent execution of other commands until the new configuration is selected and ready. The main purpose of the Stoppable Paxos is to address this bottleneck.
The same variables are used and the same messages are exchanged in case of Stoppable Paxos. It acts as ordinary Paxos till the stp command found to be chosen in some instance i. The leader will perform Phase2a actions for instances which are numbered less than i, but it will stop performing the same for instances greater than i. Simply, leader try to get stp chosen and does nothing for higher-numbered instances.