[Concurrency Control Series] #2. Optimistic vs. Pessimistic Concurrency Control To handle parallel execution safely, high-performance blockchains adopt one of two primary concurrency control models: Pessimistic or Optimistic execution. Both aim to prevent state conflicts, but they approach execution timing and computational risk from opposite directions. 1. Pessimistic Execution: Conflict Prevention First Pessimistic concurrency control analyzes transaction state access requirements before execution. - If two transactions target the same account or storage slot, the system forces one transaction to wait in queue. - Conflicting transactions are grouped into conflict-free sequential batches, eliminating re-execution overhead. - Trade-off: High resource predictability and zero failed transaction retries, but increased latency (waiting mode) during heavy state competition. 2. Optimistic Execution: Execute First, Validate Later Optimistic concurrency control assumes that conflicts are rare and executes all transactions in parallel immediately. - Transactions execute concurrently without delay, but their state updates are validated before final commitment to the ledger. - If a transaction reads stale state caused by an overlapping write, it is aborted and marked for re-execution (rerunning mode). - Trade-off: Maximum hardware utilization and sub-second latency under low conflict workloads, but wasted compute resources and retries during high-congestion state collisions. 3. The Core Engineering ChallengeChoosing between pessimistic pre-sorting and optimistic speculative execution dictates how a network performs under market volatility. Understanding these mechanics is essential for designing resilient execution layers. @RialoHQ @RialoKorea