Connection marked as broken because of SQLSTATE(08S01), ErrorCode(0)；Communications link failure

Question：

springboot 2.X多資料源配置，一段時間後連接配接無效，不能進行有效性驗證，提示：

Connection marked as broken because of SQLSTATE(08S01), ErrorCode(0);

Communications link failure

開始以為是HikariCP連接配接池配置的有問題，後面發現是程式的問題，使用EntityManager查詢操作，debug hikari也發現查詢後連接配接無法釋放

Solution:

使用@PersistenceContext？

1. springboot data jpa中的entitymanager是transaction-scoped persistence contexts
2. http://yukinami.github.io/2016/02/15/Spring%20Data%20JPA%20&%20EntityManager/
3. https://stackoverflow.com/questions/10762974/should-jpa-entity-manager-be-closed
4. validationTimeout，refer: https://github.com/brettwooldridge/HikariCP