Optimistic vs pessimistic locking?

Optimistic: 否 locks, 检查开提交 — best 当 conflicts 是罕见 (读取-heavy, web apps). Pessimistic: 锁开读取 — best 当 conflicts 是常见 (写入-heavy, financial). Optimistic 有 better 并发但 requires conflict handling. Pessimistic 是 simpler 但能够原因锁 contention 和 deadlocks.

什么如果 conflict 速率是高?

Switch 到 pessimistic locking (SELECT。.. 为 UPDATE) 或重试具有 backoff. 高 conflict 速率 means optimistic 并发是 thrashing — too 许多 retries. Also 考虑: coarser locking (锁父而非 individual rows), queueing writes, 或 partitioning 到缩减 contention.

Use optimistic 并发 control

Optimistic 并发 assumes conflicts 是罕见 — 否 locks, 仅 version checking 开提交. Learn version 列模式.

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Optimistic Concurrency Control (OCC): 读取数据无 locking, 修改本地, 开提交检查如果数据 changed 自读取. Implementation: 添加 version 列 (整数或时间戳). 开更新, 检查 WHERE version = read_version 和 increment version. 如果 0 rows updated, 某人否则 modified 它 — 重试或失败.
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SQL 格式化器 →
格式化 the UPDATE statement with the version check: UPDATE table SET col = ?, version = version + 1 WHERE id = ? AND version = ?. If the affected row count is 0, the record was modified by another transaction — handle the conflict.
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哈希计算器 →
为 distributed systems, use hash 的记录内容而非 version 数字. 此 detects 任何改变无 dedicated version 列. 开更新, 比较当前 hash 具有读取-时间 hash. 此是 useful 当你 cannot 修改模式.

常见问题

Optimistic vs pessimistic locking?: Optimistic: 否 locks, 检查开提交 — best 当 conflicts 是罕见 (读取-heavy, web apps). Pessimistic: 锁开读取 — best 当 conflicts 是常见 (写入-heavy, financial). Optimistic 有 better 并发但 requires conflict handling. Pessimistic 是 simpler 但能够原因锁 contention 和 deadlocks.
什么如果 conflict 速率是高?: Switch 到 pessimistic locking (SELECT。.. 为 UPDATE) 或重试具有 backoff. 高 conflict 速率 means optimistic 并发是 thrashing — too 许多 retries. Also 考虑: coarser locking (锁父而非 individual rows), queueing writes, 或 partitioning 到缩减 contention.