Transaction Lifecycle

Overview

Knowing how the transactions are included in a block can help understand the system of blockchain more deeply. In this document, we will delve in deeper into a step-by-step lifecycle of a transaction.

L1 Transaction Lifecycle

1. Transaction Submission: When a transaction is submitted, it undergoes a check_tx process before it's allowed into the mempool. If it's valid, it enters the mempool; If it's invalid, an error response is delivered.

2. Mempool Validation: A transaction must pass the check_tx process before it's added to the mempool. After each block is created, the mempool performs a recheck_tx on the remaining transactions, filtering out any that failed due to state changes during block execution.

3. Transaction Propagation to Validators: Once a transaction successfully enters the mempool, all nodes share the transaction through peer-to-peer (p2p) communication. This ensures delivery to the block-generating validator.

4. Block Generation (Execution): A chosen validator creates a block using the transactions in the mempool, following the cometbft rules.

L2 Transaction Lifecycle

1. Transaction Submission: When a transaction is submitted, it undergoes a check_tx process before it's allowed into the mempool. If it's valid, it enters the mempool. If it's invalid, an error response is delivered.

2. Mempool Validation: A transaction must pass the check_tx process before it's added to the mempool. After each block is created, the mempool performs a recheck_tx on the remaining transactions, filtering out any that failed due to state changes during block execution.

3. Transaction Propagation to Sequencers: Once a transaction successfully enters the mempool, all nodes share the transaction through peer-to-peer (p2p) communication. This ensures delivery to the block-generating sequencer.

4. Block Generation (Execution): Using the validated transactions, a block is generated.

5. L2 Output Submission to L1: After an epoch of blocks is generated, the L2 state root is submitted to L1 for finalization.

6. Finalization Period: This is a 7-day period set aside for the challenge period of the optimistic rollup.

7. Finalized: This is the final stage where the transaction is confirmed.

L2

+----+
| tx | -> not valid -> not received
+----+
  |   +---------+
  +-> | mempool | -> not valid -> not received
      +---------+
        |   +-----------+
        +-> | sequencer |
            +-----------+
              |   +----------+
              +-> | l2 block |-+
                  +-|--------+ |-+
                    +-|--------+ |
                      +----------+
                         |
--------------------------------------------------------
L1                       |
                         v
                   +-----------+
                   | L2 Output |
                   +-----------+
                         |
                         v
                   +----------+
                   | L1 Block |-+
                   +-|--------+ |-+
                     +-|--------+ |
                       +----------+
                         | (after finalization period)
                         v
                      finalized