[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fU87n3Ye9KhGy7CsNCpV5AXuIXmLG_liHXLc7OAFoTgQ":3},{"item":4,"related":48},{"id":5,"type":6,"title":7,"slug":8,"summary":9,"body":10,"coverUrl":11,"productScreenshots":12,"productLinks":13,"authorName":14,"authorUrl":15,"authorSubject":16,"category":17,"tags":22,"sourceLabel":39,"sourceName":40,"sourceUrl":41,"status":42,"seoTitle":7,"seoDescription":9,"canonicalUrl":39,"isFeatured":43,"sno":44,"sortOrder":45,"publishedAt":46,"updatedAt":47,"createdAt":47},"c9f4e936-9533-4b9c-a1de-f03ef09fed37","article","WAL：为什么数据库要先写日志，再写真正数据？","write-ahead-logging-wal-database-explained","WAL 要求描述数据变化的日志先于数据页持久化，让数据库可以延迟刷写并在崩溃后通过重放恢复。本文用账本和收据解释 REDO、检查点、复制与持久性设置的关系。","数据库为什么不直接把修改写进表文件，而要先写一份日志？因为真实世界的磁盘写入可能被中断：机器掉电、进程崩溃、文件系统只完成了一半写入。WAL，Write-Ahead Logging，预写式日志，提供了一条恢复线索：数据页真正落盘前，描述这次修改的日志必须先被持久化。\n\n## 先写日志，再写数据\n\n事务提交时，数据库不必立刻把所有表页和索引页都刷到磁盘，只要确保对应的 WAL 记录已经安全写入。发生崩溃后，数据库可以从日志重放尚未应用到数据页的修改，这就是 roll-forward 或 REDO 恢复。\n\n这个顺序非常关键。如果数据页先写了一部分，日志却没有记录完整，崩溃后系统就可能无法知道应该恢复什么。相反，只要日志足够完整，数据页晚一点写也可以接受。\n\n## WAL 不是普通日志文件\n\n应用日志主要帮助人类排查问题；WAL 是数据库恢复协议的一部分，记录格式、顺序、刷盘时机和检查点都有严格语义。它还可以用于复制、时间点恢复和崩溃后的重放。\n\nWAL 也有代价：日志会占用磁盘和 I\u002FO 带宽，需要归档、清理和监控。高写入量系统必须关注日志生成速度、刷盘延迟、检查点压力和复制滞后。关闭或放松持久性设置，可能换来速度，但也会改变故障后的数据保证。\n\n## AI 编程时别只写“保存成功”\n\n一个 API 返回成功，不一定代表数据已经安全写入所有层。设计订单、支付或任务队列时，需要明确事务提交点、崩溃恢复策略和重复重放行为。WAL 的思想也启发了很多系统：先记录可恢复事实，再异步整理最终结构。\n\n## 读者应该记住\n\nWAL 把数据库的可靠性建立在一条顺序上：描述变化的日志必须先于数据变化持久化。它让数据库能够快速提交、延迟刷数据，并在崩溃后通过重放恢复。\n\n资料：[PostgreSQL：Write-Ahead Logging](https:\u002F\u002Fwww.postgresql.org\u002Fdocs\u002F16\u002Fwal-intro.html)","\u002Fuploads\u002F2026-09-20\u002F6260c953-345b-4c9d-b3d6-6202c7e5539c.jpg",[],[],"Foundit","https:\u002F\u002Ffoundit.cn","foundit-ai-editorial",{"id":18,"name":19,"slug":20,"description":21},"6179d3b6-dc34-4483-9ded-3cd9f1b37a47","科普","abbreviation","介绍各领域新兴概念",[23,27,31,35],{"id":24,"name":25,"slug":26},"a202d639-99a6-488a-a712-4d4c6ffd7e15","开发","dev",{"id":28,"name":29,"slug":30},"7c76bfc2-f80f-4ee0-a95d-27bd8708b434","技术","slug",{"id":32,"name":33,"slug":34},"4c2bbea6-eab7-40a8-8447-1de478ff7749","分析","analyse",{"id":36,"name":37,"slug":38},"144abe77-0dc6-4f66-a176-20bddb1c0bfa","编程","coding",null,"PostgreSQL：Write-Ahead Logging","https:\u002F\u002Fwww.postgresql.org\u002Fdocs\u002F16\u002Fwal-intro.html","published",false,43,0,"2026-09-20T00:00:00.000Z","2026-09-20T03:58:15.082Z",[49,57,65],{"id":50,"type":6,"title":51,"slug":52,"summary":53,"coverUrl":54,"authorName":14,"sno":55,"publishedAt":46,"createdAt":56},"d0700249-defa-43a1-a66a-4455c6889072","ABI：为什么源码能编译，二进制却不能互相调用？","application-binary-interface-abi-explained","ABI 是二进制世界的调用合同，规定参数传递、对象布局、符号命名和异常处理。本文区分 ABI 与 API，解释动态库、C++ 兼容性和跨语言绑定为什么不能只看函数签名。","\u002Fuploads\u002F2026-09-20\u002F33666a48-4e8f-42a3-9ffd-f4c490498689.jpg",42,"2026-09-20T03:58:01.058Z",{"id":58,"type":6,"title":59,"slug":60,"summary":61,"coverUrl":62,"authorName":14,"sno":63,"publishedAt":46,"createdAt":64},"41d50774-50df-4e2f-b1b3-ab6d9f329726","Backpressure：生产者太快时，系统怎样不被数据淹没？","backpressure-reactive-streams-explained","Backpressure 让下游处理能力反过来影响上游生产速度，避免异步流水线靠无限缓存硬撑。本文用水管和阀门解释响应式流、需求信号、数据丢弃与容量设计，也说明它和普通限流的区别。","\u002Fuploads\u002F2026-09-20\u002F35c47792-3d4b-46ae-9375-c68e4c53330e.jpg",45,"2026-09-20T03:58:08.835Z",{"id":66,"type":6,"title":67,"slug":68,"summary":69,"coverUrl":70,"authorName":14,"sno":71,"publishedAt":46,"createdAt":72},"cd4e2aae-cbf2-4428-aab0-a6fa7911a424","Type Erasure：泛型信息为什么运行时消失了？","type-erasure-java-generics-explained","Java 的类型擦除让泛型主要承担编译期检查，生成字节码时把参数化类型替换为上界，并插入必要的转换。本文解释它带来的兼容性优势、反射限制，以及它和 Rust 单态化路线的区别。","\u002Fuploads\u002F2026-09-20\u002Fad612fe0-a1dd-4c46-a5dc-2ddfedefb22d.jpg",46,"2026-09-20T03:57:57.276Z"]