持久化功能 #376
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持久化功能 #376
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### What problem were solved in this pull request? Problem: 实现 buffer pool 支持WAL ### What is changed and how it works? buffer pool中分配和释放页面时，记录日志，并支持日志恢复。 当前buffer pool不会从文件中删除某个页面，释放是指标记为未删除。 - 在分配释放页面记录日志时，并没有等待日志完成； - 将页面数据刷新到磁盘中时，会等待对应的日志刷新到磁盘 ### Other information 1. 日志接口LogHandler转换为纯接口，并实现DiskLogHandler表示记录磁盘的日志处理器，与VacuousLogHandler，表示一个什么都不做的日志处理器，用于测试； 2. 一个LogHandler属于一个Db，Db中使用 DiskLogHandler； 3. 在创建表、索引时，需要想办法传递 LogHandler； 4. BufferPoolManager 仍为全局对象，不是Db专属的。
What problem were solved in this pull request? Problem: RecordManager 支持WAL What is changed and how it works? 每次做增删改时，都记录日志。 Other information 实现了整合buffer pool log replayer的IntegratedLogReplayer RecordScanner 不在将原始指针直接返回给调用者 为了支持（判断+更新）的原子记录更新操作，重新实现了visit_record 当前忽略了记录日志失败的情况 实际上，记录日志失败，不再应该继续执行操作 代码中使用readonly的地方，改成了 ReadWriteMode 枚举值
log entry 把unique_ptr改成vector
去掉init_header_page日志；
### What problem were solved in this pull request? Problem: bplus tree 当前不支持WAL。 ### What is changed and how it works? 增加B+树的WAL
### What problem were solved in this pull request? Problem: 文档已经陈旧，需要更新 ### What is changed and how it works? 更新readme文档，增加architecture文档，miniob-introduction文档改为简单的介绍文档。
### What problem were solved in this pull request? Problem: 合并double write buffer代码后，一些单元测试无法测试通过 主要修复了Bplus tree log测试：当一个frame涉及多个动作时，只重做了第一个动作（这个与dwb无关）； bplus tree 重做没有unpin frame； double write buffer 导致数据没有完全写入磁盘，而写入到了共享dwb文件中。
clang-format
### What problem were solved in this pull request? Problem: 增加调试日志 ### What is changed and how it works? ### Other information
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What problem were solved in this pull request?
Issue Number: close #118 #279
Problem:
当前的WAL仅记录了事务的日志，没有记录内部对象，比如record manager、B+树等的日志，导致在异常重启时，可能正常无法恢复。
What is changed and how it works?
除了记录事务日志，还记录了Buffer pool、record manager、B+树等内部数据日志，可以保证内部对象变更后断电等异常，仍然可以通过日志来恢复数据。
另外，此PR也实现了事务的回滚日志。