nested exception is com.mongodb.MongoWaitQueueFullException: Too many operations are already waiting for a connection. Max number of operations (maxWaitQueueSize) of 500 has been exceeded.

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