Socket 泄漏引起的Tomcat 宕机问题分析

在2018年4月9号下午，收到反馈：测试集群部分接口访问有问题，请求时而正常，时而超时。

最近的测试环境真的是问题多多，可是测试环境就是我搭建的，冏。查看日志发现87 这台 服务器的Tomcat 无法访问：

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2018-04-09 17:41:31,568 - [ERROR] - from org.apache.tomcat.util.net.NioEndpoint in http-nio-47001-Acceptor-0
Socket accept failed
java.io.IOException: Too many open files
at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:825)
at java.lang.Thread.run(Thread.java:745)

2018-04-09 17:41:33,168 - [ERROR] - from org.apache.tomcat.util.net.NioEndpoint in http-nio-47001-Acceptor-0
Socket accept failed
java.io.IOException: Too many open files
at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:825)
at java.lang.Thread.run(Thread.java:745)

1 Linux 文件句柄限制

报错看起来像是进程打开文件句柄的个数达到了linux的限制。而这种限制是分为系统层面的和用户层面的

1.1 系统层面

系统层面的在：/proc/sys/fs/file-max里设置

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cat /proc/sys/fs/file-max
2442976

1.2 用户层面

用户层面的限制在：/etc/security/limits.conf里设定。通过ulimit -a 查看系统允许单个进程打开的最大文件数：

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ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 192059
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 65536
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 65535
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

单个进程可以打开的最大文件数是 65536

2 lsof 显示大量open file

按照Tomcat 给出的报错信息，登录87 这台服务器检查打开的文件数，发现打开的文件超过70000:

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lsof |wc -l
75924

然后找出打开文件数最多的进程，按文件数降序排列，左边是 open file 的数量，右边是进程ID：

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lsof -n|awk '{print $2}'| sort | uniq -c | sort -nr | head
65966 25204
5374 20179
184 27275
65 5361
61 29421
16 22177
14 19751
12 22181
12 22179
12 22178

发现 25204 这个进程打开了大量的文件，已经超过了单个进程的最大文件数限制。而这个进程就是部署的java 应用对应的进程。打开的文件句柄数量已经超过Linux 限制， Tomcat 无法创建新的socket 连接。

3 can’t identify protocol

用 lsof 查看 java 应用打开的文件的时候，发现有非常多奇怪的输出：

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java    25204 nemo *516u  sock                0,6       0t0 215137625 can't identify protocol
java    25204 nemo *517u  sock                0,6       0t0 215137626 can't identify protocol
java    25204 nemo *518u  sock                0,6       0t0 215137627 can't identify protocol
java    25204 nemo *519u  sock                0,6       0t0 215137628 can't identify protocol
java    25204 nemo *520u  sock                0,6       0t0 215137629 can't identify protocol
java    25204 nemo *521u  sock                0,6       0t0 215137630 can't identify protocol
java    25204 nemo *522u  sock                0,6       0t0 215137631 can't identify protocol
java    25204 nemo *523u  sock                0,6       0t0 215137634 can't identify protocol
java    25204 nemo *524u  sock                0,6       0t0 215137635 can't identify protocol
java    25204 nemo *525u  sock                0,6       0t0 215137636 can't identify protocol
java    25204 nemo *526u  sock                0,6       0t0 215137637 can't identify protocol
java    25204 nemo *527u  sock                0,6       0t0 215137638 can't identify protocol
java    25204 nemo *528u  sock                0,6       0t0 215137639 can't identify protocol
java    25204 nemo *529u  sock                0,6       0t0 215137640 can't identify protocol
java    25204 nemo *530u  sock                0,6       0t0 215137641 can't identify protocol
java    25204 nemo *531u  sock                0,6       0t0 215137642 can't identify protocol
java    25204 nemo *532u  sock                0,6       0t0 215137644 can't identify protocol
java    25204 nemo *533u  sock                0,6       0t0 215137646 can't identify protocol

统计之后发现， can't identify protocol 这样的文件数量非常多：

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lsof -p 25204|grep "can't identify protocol"|wc -l
64214

也就是大部份打开的文件都是属于 cant' identify protocol 的文件。

4 问题定位

Google 搜索之后发现，这个 cant' identify protocol 的东东出现的原因是因为 这些 sockets 处于 CLOSED 的状态，但是却没有真正close 掉，正处于 half-close 状态。因此，如果使用 netstat 来查看socket 状态，是不会显示这些 half-close的 socket 的：

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netstat  -nat |wc -l
881

使用 netstat 的改进版本 ss 就能发现大量处于 Closed 状态的 socket:

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ss -s
Total: 76052 (kernel 76254)
TCP:   75924 (estab 123, closed 75524, orphaned 0, synrecv 0, timewait 173/0), ports 104

Transport Total     IP        IPv6
*         76254    -         -
RAW       0         0         0
UDP       9         6         3
TCP       116       80        36
INET      125       86        39
FRAG      0         0         0

接着查看内核的 socket 情况：

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cat /proc/net/sockstat
sockets: used 75724
TCP: inuse 886 orphan 0 tw 0 alloc 72134 mem 222
UDP: inuse 5 mem 0
UDPLITE: inuse 0
RAW: inuse 0
FRAG: inuse 0 memory 0

很多的 socket 处于 alloc, 只有少量的 socket 处于 inuse. 可以确认是 java 应用出现了 socket fd 的泄漏。 但是为什么会有那么多的socket 泄漏呢？

5 大胆假设

现在可以确定的是 java应用出现了问题，导致了socket 泄漏，让 Tomcat 无法建立新连接，最终宕机。既然导致问题出现的是 java 应用，那么就应该去检查应用日志。

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2018-04-09 17:41:31,491 - [ERROR] - from com.alibaba.druid.pool.DruidDataSource in Druid-ConnectionPool-CreateScheduler--4-thread-214
create connection error, url: jdbc:mysql://test-server-host:3306/db_name?readOnlyPropagatesToServer=false&rewriteBatchedStatements=true&failOverReadOnly=false&socketTimeout=6000&connectTimeout=20000&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true&characterEncoding=utf-8&autoReconnect=true
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
at sun.reflect.GeneratedConstructorAccessor169.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.Util.getInstance(Util.java:408)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:918)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:897)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:886)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2163)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2088)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:806)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.GeneratedConstructorAccessor152.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:410)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:328)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:148)
at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:211)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:142)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1423)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1477)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionTask.runInternal(DruidDataSource.java:1884)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionTask.run(DruidDataSource.java:1849)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.mysql.jdbc.exceptions.jdbc4.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 sun.reflect.GeneratedConstructorAccessor157.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:989)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2251)
at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2104)
... 21 common frames omitted
Caused by: java.net.SocketException: Too many open files
at java.net.Socket.createImpl(Socket.java:460)
at java.net.Socket.getImpl(Socket.java:520)
at java.net.Socket.setTcpNoDelay(Socket.java:980)
at com.mysql.jdbc.StandardSocketFactory.configureSocket(StandardSocketFactory.java:132)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:203)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300)
... 23 common frames omitted

2018-04-09 17:41:31,568 - [ERROR] - from org.apache.tomcat.util.net.NioEndpoint in http-nio-47001-Acceptor-0
Socket accept failed
java.io.IOException: Too many open files
at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:825)
at java.lang.Thread.run(Thread.java:745)

2018-04-09 17:41:33,168 - [ERROR] - from org.apache.tomcat.util.net.NioEndpoint in http-nio-47001-Acceptor-0
Socket accept failed
java.io.IOException: Too many open files
at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:825)
at java.lang.Thread.run(Thread.java:745)

2018-04-09 17:41:34,470 - [ERROR] - from com.alibaba.druid.pool.DruidDataSource in Druid-ConnectionPool-CreateScheduler--4-thread-216
create connection error, url: jdbc:mysql://test-server-url:3306/db_name?readOnlyPropagatesToServer=false&rewriteBatchedStatements=true&failOverReadOnly=false&socketTimeout=6000&connectTimeout=20000&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true&characterEncoding=utf-8&autoReconnect=true
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
at sun.reflect.GeneratedConstructorAccessor169.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.Util.getInstance(Util.java:408)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:918)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:897)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:886)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2163)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2088)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:806)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.GeneratedConstructorAccessor152.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:410)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:328)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:148)
at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:211)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:142)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1423)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1477)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionTask.runInternal(DruidDataSource.java:1884)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionTask.run(DruidDataSource.java:1849)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.mysql.jdbc.exceptions.jdbc4.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 sun.reflect.GeneratedConstructorAccessor157.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:989)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2251)
at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2104)
... 23 common frames omitted
Caused by: java.net.SocketException: Too many open files
at java.net.Socket.createImpl(Socket.java:460)
at java.net.Socket.getImpl(Socket.java:520)
at java.net.Socket.setTcpNoDelay(Socket.java:980)
at com.mysql.jdbc.StandardSocketFactory.configureSocket(StandardSocketFactory.java:132)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:203)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300)
... 25 common frames omitted

2018-04-09 17:41:34,769 - [ERROR] - from org.apache.tomcat.util.net.NioEndpoint in http-nio-47001-Acceptor-0
Socket accept failed
java.io.IOException: Too many open files
at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:825)
at java.lang.Thread.run(Thread.java:745)

检查日志发现，在 Tomcat 彻底挂机之前，曾经有比较大量的数据源连接池出错，无法访问 Mysql, 但是非常奇怪的是，在87 这台机器上面，是可以使用 mysql 命令行连接到测试数据库的，说明 Mysql 的连接是没有问题。

但是数据源连接就会出错！！ 真的是很奇怪，为什么连接池会报错，有没有可能是这些异常导致 socket 泄漏呢？后来，在本地运行应用，有时候会发现IDE 的控制台报错：

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2018-04-11 09:43:48,363 - [ERROR] - from com.alibaba.druid.pool.DruidDataSource in poolTaskScheduler-11
discard connection
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 100,610 milliseconds ago.  The last packet sent successfully to the server was 0 milliseconds ago.
at sun.reflect.GeneratedConstructorAccessor108.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:989)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3556)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3456)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3897)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2524)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2677)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2545)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2503)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1369)
at com.alibaba.druid.filter.FilterChainImpl.statement_executeQuery(FilterChainImpl.java:2363)
at com.alibaba.druid.filter.FilterAdapter.statement_executeQuery(FilterAdapter.java:2481)
at com.alibaba.druid.filter.FilterEventAdapter.statement_executeQuery(FilterEventAdapter.java:302)
at com.alibaba.druid.filter.FilterChainImpl.statement_executeQuery(FilterChainImpl.java:2360)
at com.alibaba.druid.proxy.jdbc.StatementProxyImpl.executeQuery(StatementProxyImpl.java:211)
at com.alibaba.druid.pool.DruidPooledStatement.executeQuery(DruidPooledStatement.java:138)
at com.taobao.tddl.atom.jdbc.TStatementWrapper.executeQuery(TStatementWrapper.java:315)
at com.taobao.tddl.group.jdbc.TGroupStatement.executeQueryOnConnection(TGroupStatement.java:549)
at com.taobao.tddl.group.jdbc.TGroupStatement$4.tryOnDataSource(TGroupStatement.java:633)
at com.taobao.tddl.group.jdbc.TGroupStatement$4.tryOnDataSource(TGroupStatement.java:615)
at com.taobao.tddl.group.dbselector.AbstractDBSelector.tryOnDataSourceHolder(AbstractDBSelector.java:155)
at com.taobao.tddl.group.dbselector.OneDBSelector.tryExecuteInternal(OneDBSelector.java:52)
at com.taobao.tddl.group.dbselector.AbstractDBSelector.tryExecute(AbstractDBSelector.java:405)
at com.taobao.tddl.group.dbselector.AbstractDBSelector.tryExecute(AbstractDBSelector.java:412)
at com.taobao.tddl.group.jdbc.TGroupStatement.executeQuery(TGroupStatement.java:488)
at com.taobao.tddl.group.jdbc.TGroupStatement.executeInternal(TGroupStatement.java:131)
at com.taobao.tddl.group.jdbc.TGroupStatement.execute(TGroupStatement.java:101)
at com.taobao.tddl.repo.mysql.spi.My_JdbcHandler.executeQuery(My_JdbcHandler.java:521)
at com.taobao.tddl.repo.mysql.spi.My_Cursor.init(My_Cursor.java:106)
at com.taobao.tddl.repo.mysql.handler.QueryMyHandler.handle(QueryMyHandler.java:89)
at com.taobao.tddl.executor.AbstractGroupExecutor.executeInner(AbstractGroupExecutor.java:47)
at com.taobao.tddl.executor.AbstractGroupExecutor.execByExecPlanNode(AbstractGroupExecutor.java:36)
at com.taobao.tddl.executor.TopologyExecutor.execByExecPlanNode(TopologyExecutor.java:66)
at com.taobao.tddl.executor.MatrixExecutor.execByExecPlanNodeByOne(MatrixExecutor.java:670)
at com.taobao.tddl.executor.MatrixExecutor.execByExecPlanNode(MatrixExecutor.java:659)
at com.taobao.tddl.executor.MatrixExecutor.execute(MatrixExecutor.java:137)
at com.taobao.tddl.matrix.jdbc.TConnection.executeSQL(TConnection.java:241)
at com.taobao.tddl.matrix.jdbc.TPreparedStatement.executeSQL(TPreparedStatement.java:64)
at com.taobao.tddl.matrix.jdbc.TStatement.executeInternal(TStatement.java:133)
at com.taobao.tddl.matrix.jdbc.TPreparedStatement.execute(TPreparedStatement.java:49)
at sun.reflect.GeneratedMethodAccessor148.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59)
at com.sun.proxy.$Proxy102.execute(Unknown Source)
at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:63)
at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63)
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:325)
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
at sun.reflect.GeneratedMethodAccessor146.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49)
at fastfish.interceptor.DbLogInterceptor.intercept(DbLogInterceptor.java:49)
at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61)
at com.sun.proxy.$Proxy100.query(Unknown Source)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
at sun.reflect.GeneratedMethodAccessor145.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:434)
at com.sun.proxy.$Proxy87.selectList(Unknown Source)
at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:231)
at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:128)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:68)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
at com.sun.proxy.$Proxy124.selectAll(Unknown Source)
at fastfish.services.BusinessService.getAll(BusinessService.java:73)
at fastfish.services.BusinessService.loadDB(BusinessService.java:38)
at sun.reflect.GeneratedMethodAccessor190.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:65)
at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset$$$capture(FutureTask.java:308)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
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: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3008)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3466)
... 83 common frames omitted

是数据池连接出错。但是我本地的应用确实是可以访问测试数据库的， 比较有趣的异常就是

1

Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.

数据还没有读完， Connection 就丢了。为什么会 lost connection 呢，可能数据库出问题，也可能是网络出了问题。

我还能从数据库读到数据，说明数据库没问题的，兼之这个异常只是偶尔出现，所以可能就是网络出问题了。

如此说来，是否可能是因为测试环境网络不稳定，连接池无法和 Mysql 保持连接，在丢掉 Connection 之后，连接池重新发起连接，但是因为网络不稳定又丢掉了Connection, 不断循环这个过程，导致建立的 socket 连接越 来越多，但是建立的 socket 很快就被Close 掉了，内核又没有把这些 Close 掉的 socket 资源回收掉，因此打开的 socket 文件越来越多，最后导致 Tomcat 因为打开的文件过多无法建立新的 socket 连接。

6 小心求证

如果连接池真的不断尝试连接Mysql 的话，必定会建立很多的连接，而Mysql 是会将这些记录保存下来的，检查Mysql 的变量：

查看Mysql 的文档关于 Connection 和 Thread_connected 的说明：

  • Connections

    The number of connection attempts (successful or not) to the MySQL server.

  • Threads_connected

    The number of currently open connections.

也就是说，当时共有20000 多的连接请求，但是真正被 Mysql accpet 并且服务的只有 28 个连接。看来的确是因为连接池的连接导致 socket 泄漏

6.1 更新

和运维同学沟通之后，发现丢连接的原因不是网络不稳定，而是测试集群都是虚拟机，内存 用光，导致无法建立新的连接，内核释放一部分资源之后又可以建立连接了。内存用完，我能怎么办，我也很无奈。

7 解决方法

虽说基本确定了 socket 泄漏的源头，但是对于内核为什么无法回收已经关闭 socket 的原因依然不明确。

最令人百思不得其解的是，部署了应用的测试服务器有两台，另外一 台服务器也有同样的连接池问题，但是却没有出现 socket 泄漏问题， 出现泄漏的只有 87 这台机器。真的令人费解. 所以最后解决方法就是撤下 87 服务器的应用，换一台服务器来部署。

新的服务器部署应用之后虽说也有同样的数据库连接池异常，但是却没有出现 socket 泄漏，初步定位是 87这台机器的内核环境存在问题。

8 参考