java项目记一次内存溢出Java heap space

一、具体报错信息：

Caused by: java.sql.SQLException: Java heap space
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:970)
    at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:387)
    at com.alibaba.druid.pool.DruidPooledPreparedStatement.execute(DruidPooledPreparedStatement.java:498)
    at org.apache.shardingsphere.shardingjdbc.executor.SQLExecuteCallbackFactory$2.executeSQL(SQLExecuteCallbackFactory.java:62)
    at org.apache.shardingsphere.shardingjdbc.executor.SQLExecuteCallbackFactory$2.executeSQL(SQLExecuteCallbackFactory.java:58)
    at org.apache.shardingsphere.sharding.execute.sql.execute.SQLExecuteCallback.execute0(SQLExecuteCallback.java:82)
    at org.apache.shardingsphere.sharding.execute.sql.execute.SQLExecuteCallback.execute(SQLExecuteCallback.java:58)
    at org.apache.shardingsphere.underlying.executor.engine.ExecutorEngine.syncExecute(ExecutorEngine.java:97)
    at org.apache.shardingsphere.underlying.executor.engine.ExecutorEngine.parallelExecute(ExecutorEngine.java:93)
    at org.apache.shardingsphere.underlying.executor.engine.ExecutorEngine.execute(ExecutorEngine.java:76)
    at org.apache.shardingsphere.sharding.execute.sql.execute.SQLExecuteTemplate.execute(SQLExecuteTemplate.java:68)
    at org.apache.shardingsphere.sharding.execute.sql.execute.SQLExecuteTemplate.execute(SQLExecuteTemplate.java:51)
    at org.apache.shardingsphere.shardingjdbc.executor.AbstractStatementExecutor.executeCallback(AbstractStatementExecutor.java:129)
    at org.apache.shardingsphere.shardingjdbc.executor.PreparedStatementExecutor.execute(PreparedStatementExecutor.java:148)
    at org.apache.shardingsphere.shardingjdbc.jdbc.core.statement.ShardingPreparedStatement.execute(ShardingPreparedStatement.java:145)
    at sun.reflect.GeneratedMethodAccessor94.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59)
    at com.sun.proxy.$Proxy178.execute(Unknown Source)
    at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64)
    at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
    at sun.reflect.GeneratedMethodAccessor109.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.Plugin.invoke(Plugin.java:63)
    at com.sun.proxy.$Proxy176.query(Unknown Source)
    at com.baomidou.mybatisplus.core.executor.MybatisSimpleExecutor.doQuery(MybatisSimpleExecutor.java:67)
    at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
    at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:426)

二、问题出现原因：

由于表数量会很大，我就在在项目中使用了shadingphere进行分表，它的分页查询每次都取取出所有的数据，进行排序，分页。导致内存不足。

想到解决办法：

1）代码层面，优化sql查询。如优化分页查询的方式和设置数据库连接使用useCursorFetch=true&defaultFetchSize=100。---未尝试，planB

2）既然内存问题，物理办法增大，先试一下。

三、分析方案并且尝试

1）查看java的jvm启动参数。

2）解读参数并且分析报错原因。

查了一下，启动java项目时jvm的默认分配：JVM启动时，JVM堆会自动设置heap size值。通常情况下，初始空间（即-Xms）默认值是物理内存的1/64，最大空间是物理内存的1/4。可以利用JVM提供的-Xmn -Xms -Xmx等选项可进行设置。

查看本物理机的内存：

cat /proc/meminfo | grep MemTotal

本物理机的内存只有4G，最大时只有1G，估计进程超过了1G了。验证一下。

3）先进行1G的分配，验证一下1G够不够。

nohup /usr/local/jdk1.8.0_91/bin/java -jar  -Xms2048m -Xmx2048m -Xss1024K -XX:PermSize=128m -XX:MaxPermSize=256m  /data/apps/xxx/xxx.jar --spring.config.location=/data/apps/xxx/config/ > /data/logs/xxx/xxx.log 2>&1 &

4)重启运行项目，重现报错，并且查看进行使用内存大小。

## 查看当前java程序中内个对象的数量和占用空间
jmap -histo 9882 | head -n10

5）果然，分配的内存没有超过1G。

6）分配2G内存

7）运行没报错，具体内存消耗：1.2G左右。

四、总结

这个问题算是解决了，2G分配内存能接受。

但项目中的count的消耗时间需要解决，多人使用也会叠加内存，所以，还是需要在代码中优化，准备尝试第一种解决方案。

原文地址：https://blog.csdn.net/baidu_35287211/article/details/115861567?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522168475001216800227455128%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fall.%2522%257D&request_id=168475001216800227455128&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~first_rank_ecpm_v1~rank_v31_ecpm-14-115861567-null-null.142^v87^insert_down1,239^v2^insert_chatgpt&utm_term=java%E4%BC%98%E5%8C%96