The in-memory sort operation can be made effective (from storage and computation standpoints) under the fact that each list li is ordered by itself.
如果每个列表Li由自已排序，那么内存内的排序操作(从存储和计算的角度)可以变得很有效。
2
Cleanup: This operation is used for storage maintenance.
cleanup：该操作用于存储维护。
3
Successfully posting to the log is also considered a commit (the data is safely stored to persistent storage), allowing the database operation to complete and continue.