Search the library

If each transaction sees a snapshot where another row satisfies a rule, they may update different rows and both commit, leaving the combined invariant false. Use a constraint, lock a shared coordination row, or use serializable isolation with whole-transaction retry. Exact Repeatable Read semantics differ by engine.

A committed first attempt advances the validator, so a repeat with the old validator may fail with 412. Use a separate scoped idempotency contract when retries must recover the original result.

Modern Java ConcurrentHashMap does not use the fixed lock segments from older implementations. It uses non-blocking reads and coordinates updates with CAS and synchronization at individual bins when needed. This allows unrelated keys to make progress concurrently. It protects map operations, not a multi-key transaction or mutable values stored inside it.

With three brokers and min.insync.replicas=2, acks=all requires the current in-sync replica set to meet the minimum. If the ISR falls to one, writes are rejected rather than acknowledged with reduced replication. acks=1 favors availability but risks losing leader-only writes if that leader fails before replication.

Measure elapsed time locally with nanoTime and give each stage only the shared budget remaining. Expiry stops admission of more work; it does not prove a remote write was cancelled.

Volatile gives visibility and ordering for a field but does not make compound read-modify-write operations atomic. Synchronized protects a critical section and its invariants using a monitor. AtomicInteger provides atomic operations such as increment-and-get for one integer; it does not make a group of fields update transactionally.