有一个 Spring Boot 应用程序可以将通过 API 接收到的大量数据传输到远程数据库（MySQL）。我使用 HikariCP 作为连接池，下面是它在应用启动时的配置：
HikariPool-1 - configuration:
allowPoolSuspension.............false
autoCommit......................false
catalog.........................none
connectionInitSql...............none
connectionTestQuery.............none
connectionTimeout...............30000
dataSource......................none
dataSourceClassName.............none
dataSourceJNDI..................none
dataSourceProperties............{password=<masked>}
driverClassName................."com.mysql.cj.jdbc.Driver"
healthCheckProperties...........{}
healthCheckRegistry.............none 2019-02-21 13:00:32:351 [main] DEBUG c.z.h.HikariConfig.logConfiguration() - idleTimeout.....................600000
initializationFailTimeout.......1
isolateInternalQueries..........false
jdbcUrl.........................jdbc:mysql://url/db_name?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC&failOverReadOnly=false
leakDetectionThreshold..........0
maxLifetime.....................1800000
maximumPoolSize.................10
metricRegistry..................none
metricsTrackerFactory...........none
minimumIdle.....................10
password........................<masked>
poolName........................"HikariPool-1"
readOnly........................false
registerMbeans..................false
scheduledExecutor...............none
schema..........................none
threadFactory...................internal
transactionIsolation............default
username........................"name"
validationTimeout...............5000
在运行过程中，会出现一个日志：HikariPool-1 - Pool stats (total=10, active=0, idle=10, waiting=0)
工作几分钟后，抛出异常：
2019-02-21 12:56:22:323 [HikariPool-1 connection closer] DEBUG c.z.h.p.PoolBase.quietlyCloseConnection() - HikariPool-1 - Closing connection com.mysql.cj.jdbc.ConnectionImpl@4169569c: (connection is dead)
2019-02-21 12:56:22:327 [HikariPool-1 connection adder] DEBUG c.z.h.p.HikariPool.createPoolEntry() - HikariPool-1 - Cannot acquire connection from data source
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:835)
at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455)
at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240)
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)
at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:136)
at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:369)
at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:198)
at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:467)
at com.zaxxer.hikari.pool.HikariPool.access$100(HikariPool.java:71)
at com.zaxxer.hikari.pool.HikariPool$PoolEntryCreator.call(HikariPool.java:706)
at com.zaxxer.hikari.pool.HikariPool$PoolEntryCreator.call(HikariPool.java:692)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:91)
at com.mysql.cj.NativeSession.connect(NativeSession.java:152)
at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:955)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:825)
... 14 common frames omitted
Caused by: java.net.ConnectException: В соединении отказано (Connection refused)
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at com.mysql.cj.protocol.StandardSocketFactory.connect(StandardSocketFactory.java:155)
at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:65)
... 17 common frames omitted
2019-02-21 12:56:28:238 [HikariPool-1 housekeeper] DEBUG c.z.h.p.HikariPool.logPoolState() - HikariPool-1 - Pool stats (total=0, active=0, idle=0, waiting=1)
2019-02-21 12:56:30:417 [HikariPool-1 connection adder] DEBUG c.z.h.p.HikariPool.createPoolEntry() - HikariPool-1 - Cannot acquire connection from data source
试图安装max-lifetime: 25800, maximum-pool-size: 20, minimum-idle: 0, idle-timeout: 30000- 结果总是一样的。可能是什么问题呢？
升级版：
从数据库输出超时：
connect_timeout 10
deadlock_timeout_long 50000000
deadlock_timeout_short 10000
delayed_insert_timeout 300
innodb_lock_wait_timeout 50
innodb_rollback_on_timeout OFF
interactive_timeout 28800
lock_wait_timeout 31536000
net_read_timeout 30
net_write_timeout 600
slave_net_timeout 3600
thread_pool_idle_timeout 60
wait_timeout 28800
UPD2。
在工作过程中，出现日志：
[yourPoolName connection closer] DEBUG c.z.h.p.PoolBase.quietlyCloseConnection() - yourPoolName - Closing connection com.mysql.cj.jdbc.ConnectionImpl@742e0612: (connection has passed maxLifetime)
[yourPoolName connection adder] DEBUG c.z.h.p.HikariPool.call() - yourPoolName - Added connection com.mysql.cj.jdbc.ConnectionImpl@16e8fb27
UPD3
原来 MySQL 在远程服务器上崩溃了。提供商说内存不足。什么会阻塞记忆？也许某种 MySQL 缓存？
