Tools

2 phase commit With different failures

Procedure

Use the steps below to run through the baseline commit and then each failure scenario in sequence. The simulator UI consists of:

  • Canvas (center): visual nodes/links/messages
  • Control Panel (left): Start/Reset buttons, timeouts, clock speed, scenario selector
  • State & Log Panel (right): per-node state, protocol log

A. Setup & Baseline Commit

  1. Load the Simulator
    • Open the simulation in your browser. You’ll see five nodes: C (coordinator) in pink, P₁–P₄ (participants) in blue, connected by solid gray links.
  2. Verify Defaults
    • Vote Timeout = 5000 ms; Decision Timeout = 5000 ms; Clock 1×.
  3. Start a Clean Run
    • Click Reset Simulation. Confirm all node states read INIT and log is empty.
  4. Execute Normal Commit
    • Click Start Transaction.
    • Watch in the log:
      • C → PREPARE → P₁–P₄ → each logs READY and replies VOTE_COMMIT
      • C collects all votes, logs COMMIT, broadcasts GLOBAL_COMMIT
      • P₁–P₄ each log COMMIT, send ACK → C completes.
    • Confirm all four participants end in COMMITTING → DONE and coordinator state DONE.

B. Progress-Based Failure Scenarios

Use the Scenario dropdown to pick each task in order. You may only inject the allowed failures per scenario.

Scenario 1: Single Participant Crash

  • Goal: Force GLOBAL_ABORT by crashing exactly one participant before it votes.
  • Allowed: 1 participant crash.
  • Steps:
    1. Reset the sim.
    2. Select “Single Participant Crash.” Read instructions.
    3. Click Start Transaction.
    4. As soon as any one P (e.g. P₂) receives PREPARE but before it sends VOTE_COMMIT, click that node to crash it (it’ll gray out).
    5. Wait for Vote‐Timeout → C must decide GLOBAL_ABORT.
    6. Check: All P₁, P₃, P₄ log ABORT; coordinator logs ABORT.
    7. Simulator flashes “Scenario Passed!” and unlocks the next scenario.

Scenario 2: Dropped Vote Message

  • Goal: Force ABORT by dropping exactly one VOTE_COMMIT.
  • Allowed: 1 link down.
  • Steps:
    1. Click “Dropped Vote Message” in the Scenario dropdown.
    2. Reset.
    3. Start Transaction.
    4. Immediately after C sends PREPARE, click the link between C and one P (e.g. P₃) to bring it down (dashed red).
    5. Wait for Vote‐Timeout → C must GLOBAL_ABORT.
    6. Verify: P₃ never sent a vote; P₁, P₂, P₄ receive GLOBAL_ABORT and abort.
    7. “Scenario Passed!” appears; Scenario 3 unlocked.

Enjoy exploring how 2PC handles failures in addtional scenarios!