Pesimistic locking sequence diagram

optimistic-locking.md

sequenceDiagram
    participant John as John
    participant DB as Database
    participant Mary as Mary

    John->>DB: begin_transaction()
    Note over DB: Lock acquired on source & dest accounts

    Mary->>DB: begin_transaction()
    Note over Mary,DB: Waiting for lock release

    John->>DB: debit_source_account()
    John->>DB: credit_destination_account()
    Note over DB: Lock still held

    John-->>John: Error occurs
    John->>DB: rollback_transaction()
    Note over DB: Lock released

    Note over Mary,DB: Lock acquired on source & dest accounts
    Mary->>DB: debit_source_account()
    Mary->>DB: credit_destination_account()
    Note over DB: Lock still held
    Mary->>DB: commit_transaction()
    Note over DB: Lock released

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