----------------SQL优化------------------
---------------JVM优化-------------------
--------------hashmap的原理-----------
-----------hashmap碰撞解决办法------
https://www.cnblogs.com/weigy/p/12571648.html
----------mysql数据库隔离级别---------
https://www.jianshu.com/p/48fbf17e9e5c
https://www.cnblogs.com/zhoujinyi/p/3437475.html
----------mysql乐观锁和悲观锁--------
https://www.cnblogs.com/weigy/p/12567667.html