application.yml 添加后两行配置，增加连接池数量
data:
mongodb:
host: ***
database: ***
port: 27017
username: ***
password: ***
authenticationDatabase: ***
connections-per-host: 10000
min-connections-per-host: 200
原文：https://www.cnblogs.com/guangxiang/p/12375326.html