这里从DBImpl::MaybeScheduleFlushOrCompaction开始讲起。DBImpl::MaybeScheduleFlushOrCompaction可能会scheduleDBImpl::BGWorkFlush和DBImpl::BGWorkCompaction。这里主要看Compaction。Flush部分见{%post_linkStorage/'RocksDB代码分析——Flush流程'%}DBImpl::BGWorkCo