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Created December 12, 2020 03:16
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数据库系统中的日志
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Logs in Database Management System.md

日志(LOG, Journal)是持久化的核心, 是基础, 是必须.

根据日志的用途, 可以分成两类:

  1. Write Ahead Log, 将数据持久化在日志中, 日志持久化, 即代表数据持久化. 日志持久化之后, 后期再将数据转存到它们应该放的地方.
  2. Write Behind Log, Commit Log, 先将数据直接写到它们应该放的地方, 然后通过日志来确认.

WAL 在理想情况下, 单次写的延迟较小, 但有写放大问题, 因为必须有"转存"步骤.

WBL 单次写延迟大, 因为每一次写请求涉及两次持久化, 但没有写放大问题.

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