30、 Modern storage system (management database and distributed storage system)

One 、 Database transactions

Large scale data , Efficient atomic operation

1、 Index and query optimization

Two 、 The realization of database

Virtual disk （ file ） Data structure on

1、 hold SQL The query is translated into read,write,lseek,fsync Call to

2、 concurrency control （ Transaction processing ）

3、 ... and 、 The foundation of Distributed Systems

Distributed consensus protocol

1、 Copy state machine

2、RaftScope Visualization Tool

3、 ... and 、 Distributed data model ：Key-Valie

LevelDB Key-Value Storage

1、 Single process （ Multithreading ）, Press Key Sort

2、 Support transactions

3、 Support for snapshots （ Instant read-only snapshot of a state ）

A way of implementation ： journal

1、snapshot() Returns the length of the current file

2、put(k,v) All directly k,v Append to the end of the file

（1） Very efficient

3、get(k,v) Traverse the entire file

（1） Extremely inefficient （ Reading amplification ）

Four 、Log-structured Merge（LSM）Tree

A simulated memory hierarchy

1、 Write direct append to log file

2、Crash safe; Not too fast

Solve read amplification

1、 Now maintain in memory log Real time data structure