Three Phase Commit

CS380D Distributed Computing I — Project 1

Name : Tian Zhang
ID: tz3272

Name: Bradley Beth ID: bethbg

============================================================================== README

ThreePhaseCommit is a java-based controller that takes in 1 argument—a file containing the controller script (e.g., script1.txt).

The allowable commands are: • createProcesses NUM_PROCESSES • kill PROCESS_ID • killAll • killLeader • revive PROCESS_ID • reviveLast • reviveAll • partialMessage PROCESS_ID NUM_MSGS • resumeMessages PROCESS_ID • allClear • rejectNextChange PROCESS_ID • add SONG_TITLE SONG_URL • edit SONG_TITLE NEW_SONG_TITLE NEW_SONG_URL • remove SONG_TITLE • wait

The Node class contains the code for each process. These processes are created by ThreePhaseCommit using ProcessBuilder. Each requires arguments specifying a configuration filename, a DT-Log filename, and {new|revive}—in that order.

add, edit, and remove commands may also be batched by placing them in the file ActionList.txt.

============================================================================== Mistake in reading

The mistake is that we do need to log the precommit.

Without logging precommit :

1. Coordinator writes Commit to its logs after getting ACKs from everyone, but dies before sending commits to anyone.

2. Now the Coordinator dies. All the participants timeout, then run the election protocol electing the operational process with the lowest PID as the new coordinator. The state of all participants is "COMMITABLE".

3. At this point, all the participants die, thereby inducing total failure. Now all the participants start recovering except the coordinator. Since no precommit was logged, they see their votes and move to the state "UNCERTAIN".

4. Everyone is in uncertain state so the decision taken is abort.

5. When the coordinator wakes up, there is an inconsistency in the decision taken by the coordinator and the decision taken by the participants.