背景：
Java 功能压测的时候,执行数据库sql缓慢分析报错，使用的Sharding-jdbc，进行了分库分表。高TPS访问时，遇到了瓶颈，
报错：
"http-bio-8088-exec-3762" - Thread t@188077
java.lang.Thread.State: BLOCKED
at sun.security.provider.NativePRNG$RandomIO.implNextBytes(NativePRNG.java:543)
- waiting to lock <404ee8b2> (a java.lang.Object) owned by "http-bio-8088-exec-3552" t@187443
at sun.security.provider.NativePRNG$RandomIO.access$400(NativePRNG.java:331)
at sun.security.provider.NativePRNG.engineNextBytes(NativePRNG.java:220)
at java.security.SecureRandom.nextBytes(SecureRandom.java:468)
at java.util.UUID.randomUUID(UUID.java:145)
at io.shardingsphere.core.event.ShardingEvent.<init>(ShardingEvent.java:32)
at io.shardingsphere.core.event.executor.SQLExecutionEvent.<init>(SQLExecutionEvent.java:34)
at io.shardingsphere.core.event.executor.DMLExecutionEvent.<init>(DMLExecutionEvent.java:34)
at io.shardingsphere.core.event.executor.SQLExecutionEventFactory.createEvent(SQLExecutionEventFactory.java:51)
at io.shardingsphere.core.executor.sql.execute.SQLExecuteCallback.execute0(SQLExecuteCallback.java:89)
at io.shardingsphere.core.executor.sql.execute.SQLExecuteCallback.execute(SQLExecuteCallback.java:69)
at io.shardingsphere.core.executor.ShardingExecuteEngine.syncGroupExecute(ShardingExecuteEngine.java:182)
at io.shardingsphere.core.executor.ShardingExecuteEngine.groupExecute(ShardingExecuteEngine.java:158)
at io.shardingsphere.core.executor.sql.execute.SQLExecuteTemplate.executeGroup(SQLExecuteTemplate.java:71)
at io.shardingsphere.core.executor.sql.execute.SQLExecuteTemplate.executeGroup(SQLExecuteTemplate.java:54)
at io.shardingsphere.shardingjdbc.executor.AbstractStatementExecutor.executeCallback(AbstractStatementExecutor.java:122)
at io.shardingsphere.shardingjdbc.executor.PreparedStatementExecutor.execute(PreparedStatementExecutor.java:161)
at io.shardingsphere.shardingjdbc.jdbc.core.statement.ShardingPreparedStatement.execute(ShardingPreparedStatement.java:139)
at org.apache.ibatis.executor.statement.PreparedStatementHandler.update(PreparedStatementHandler.java:46)
at org.apache.ibatis.executor.statement.RoutingStatementHandler.update(RoutingStatementHandler.java:74)
at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:50)
at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117)
at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:76)
at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:198)
at sun.reflect.GeneratedMethodAccessor501.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:433)
at com.sun.proxy.$Proxy49.update(Unknown Source)
at org.mybatis.spring.SqlSessionTemplate.update(SqlSessionTemplate.java:294)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:62)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
at com.sun.proxy.$Proxy79.updateByAgentNoAndTradeOrderNo(Unknown Source)
主要原因是底层 使用了java.util.UUID.randomUUID，其中sun.security.provider.NativePRNG$RandomIO.implNextBytes 获取随机数，上锁了，block.
目前解决方案：
在tomcat 配置中 -Djava.security.egd=file:/dev/./urandom
