低版本Druid连接池+MySQL驱动8.0导致线程阻塞、性能受限

目录

• 现象
• 根因分析
• getLastPacketReceivedTimeMs()方法调用时机
• 解决方案

现象

应用升级MySQL驱动8.0后，在并发量较高时，查看监控打点，Druid连接池拿到连接并执行SQL的时间大部分都超过200ms

对系统进行压测，发现出现大量线程阻塞的情况，线程dump信息如下：

"http-nio-5366-exec-48" #210 daemon prio=5 os_prio=0 tid=0x00000000023d0800 nid=0x3be9 waiting for monitor entry [0x00007fa4c1400000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader.loadClass(TomcatEmbeddedWebappClassLoader.java:66)
        - waiting to lock <0x0000000775af0960> (a java.lang.Object)
        at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1186)
        at com.alibaba.druid.util.Utils.loadClass(Utils.java:220)
        at com.alibaba.druid.util.MySqlUtils.getLastPacketReceivedTimeMs(MySqlUtils.java:372)

根因分析

public class MySqlUtils {

    public static long getLastPacketReceivedTimeMs(Connection conn) throws SQLException {
        if (class_connectionImpl == null && !class_connectionImpl_Error) {
            try {
                class_connectionImpl = Utils.loadClass("com.mysql.jdbc.MySQLConnection");
            } catch (Throwable error){
                class_connectionImpl_Error = true;
            }
        }

        if (class_connectionImpl == null) {
            return -1;
        }

        if (method_getIO == null && !method_getIO_error) {
            try {
                method_getIO = class_connectionImpl.getMethod("getIO");
            } catch (Throwable error){
                method_getIO_error = true;
            }
        }

        if (method_getIO == null) {
            return -1;
        }

        if (class_MysqlIO == null && !class_MysqlIO_Error) {
            try {
                class_MysqlIO = Utils.loadClass("com.mysql.jdbc.MysqlIO");
            } catch (Throwable error){
                class_MysqlIO_Error = true;
            }
        }

        if (class_MysqlIO == null) {
            return -1;
        }

        if (method_getLastPacketReceivedTimeMs == null && !method_getLastPacketReceivedTimeMs_error) {
            try {
                Method method = class_MysqlIO.getDeclaredMethod("getLastPacketReceivedTimeMs");
                method.setAccessible(true);
                method_getLastPacketReceivedTimeMs = method;
            } catch (Throwable error){
                method_getLastPacketReceivedTimeMs_error = true;
            }
        }

        if (method_getLastPacketReceivedTimeMs == null) {
            return -1;
        }

        try {
            Object connImpl = conn.unwrap(class_connectionImpl);
            if (connImpl == null) {
                return -1;
            }

            Object mysqlio = method_getIO.invoke(connImpl);
            Long ms = (Long) method_getLastPacketReceivedTimeMs.invoke(mysqlio);
            return ms.longValue();
        } catch (IllegalArgumentException e) {
            throw new SQLException("getLastPacketReceivedTimeMs error", e);
        } catch (IllegalAccessException e) {
            throw new SQLException("getLastPacketReceivedTimeMs error", e);
        } catch (InvocationTargetException e) {
            throw new SQLException("getLastPacketReceivedTimeMs error", e);
        }
    }

MySqlUtils中的getLastPacketReceivedTimeMs()方法会加载com.mysql.jdbc.MySQLConnection这个类，但在MySQL驱动8.0中类名改为com.mysql.cj.jdbc.ConnectionImpl，所以MySQL驱动8.0中加载不到com.mysql.jdbc.MySQLConnection

getLastPacketReceivedTimeMs()方法实现中，如果Utils.loadClass("com.mysql.jdbc.MySQLConnection")加载不到类并抛出异常，会修改变量class_connectionImpl_Error，下次调用不会再进行加载

public class Utils {

    public static Class<?> loadClass(String className) {
        Class<?> clazz = null;

        if (className == null) {
            return null;
        }

        try {
            return Class.forName(className);
        } catch (ClassNotFoundException e) {
            // skip
        }

        ClassLoader ctxClassLoader = Thread.currentThread().getContextClassLoader();
        if (ctxClassLoader != null) {
            try {
                clazz = ctxClassLoader.loadClass(className);
            } catch (ClassNotFoundException e) {
                // skip
            }
        }

        return clazz;
    }

但是，在Utils的loadClass()方法中同样catch了ClassNotFoundException，这就导致loadClass()在加载不到类的时候，并不会抛出异常，从而会导致每调用一次getLastPacketReceivedTimeMs()方法，就会加载一次MySQLConnection这个类

线程dump信息中可以看到是在调用TomcatEmbeddedWebappClassLoader的loadClass()方法时，导致线程阻塞的

public class TomcatEmbeddedWebappClassLoader extends ParallelWebappClassLoader {

 public Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
  synchronized (JreCompat.isGraalAvailable() ? this : getClassLoadingLock(name)) {
   Class<?> result = findExistingLoadedClass(name);
   result = (result != null) ? result : doLoadClass(name);
   if (result == null) {
    throw new ClassNotFoundException(name);
   }
   return resolveIfNecessary(result, resolve);
  }
 }

这是因为TomcatEmbeddedWebappClassLoader在加载类的时候，会加synchronized锁，这就导致每调用一次getLastPacketReceivedTimeMs()方法，就会加载一次com.mysql.jdbc.MySQLConnection，而又始终加载不到，在加载类的时候会加synchronized锁，所以会出现线程阻塞，性能下降的现象

getLastPacketReceivedTimeMs()方法调用时机

public abstract class DruidAbstractDataSource extends WrapperAdapter implements DruidAbstractDataSourceMBean, DataSource, DataSourceProxy, Serializable {

    protected boolean testConnectionInternal(DruidConnectionHolder holder, Connection conn) {
        String sqlFile = JdbcSqlStat.getContextSqlFile();
        String sqlName = JdbcSqlStat.getContextSqlName();

        if (sqlFile != null) {
            JdbcSqlStat.setContextSqlFile(null);
        }
        if (sqlName != null) {
            JdbcSqlStat.setContextSqlName(null);
        }
        try {
            if (validConnectionChecker != null) {
                boolean valid = validConnectionChecker.isValidConnection(conn, validationQuery, validationQueryTimeout);
                long currentTimeMillis = System.currentTimeMillis();
                if (holder != null) {
                    holder.lastValidTimeMillis = currentTimeMillis;
                    holder.lastExecTimeMillis = currentTimeMillis;
                }

                if (valid && isMySql) { // unexcepted branch
                    long lastPacketReceivedTimeMs = MySqlUtils.getLastPacketReceivedTimeMs(conn);
                    if (lastPacketReceivedTimeMs > 0) {
                        long mysqlIdleMillis = currentTimeMillis - lastPacketReceivedTimeMs;
                        if (lastPacketReceivedTimeMs > 0 //
                                && mysqlIdleMillis >= timeBetweenEvictionRunsMillis) {
                            discardConnection(holder);
                            String errorMsg = "discard long time none received connection. "
                                    + ", jdbcUrl : " + jdbcUrl
                                    + ", jdbcUrl : " + jdbcUrl
                                    + ", lastPacketReceivedIdleMillis : " + mysqlIdleMillis;
                            LOG.error(errorMsg);
                            return false;
                        }
                    }
                }

                if (valid && onFatalError) {
                    lock.lock();
                    try {
                        if (onFatalError) {
                            onFatalError = false;
                        }
                    } finally {
                        lock.unlock();
                    }
                }

                return valid;
            }

            if (conn.isClosed()) {
                return false;
            }

            if (null == validationQuery) {
                return true;
            }

            Statement stmt = null;
            ResultSet rset = null;
            try {
                stmt = conn.createStatement();
                if (getValidationQueryTimeout() > 0) {
                    stmt.setQueryTimeout(validationQueryTimeout);
                }
                rset = stmt.executeQuery(validationQuery);
                if (!rset.next()) {
                    return false;
                }
            } finally {
                JdbcUtils.close(rset);
                JdbcUtils.close(stmt);
            }

            if (onFatalError) {
                lock.lock();
                try {
                    if (onFatalError) {
                        onFatalError = false;
                    }
                } finally {
                    lock.unlock();
                }
            }

            return true;
        } catch (Throwable ex) {
            // skip
            return false;
        } finally {
            if (sqlFile != null) {
                JdbcSqlStat.setContextSqlFile(sqlFile);
            }
            if (sqlName != null) {
                JdbcSqlStat.setContextSqlName(sqlName);
            }
        }
    }

只有DruidAbstractDataSource的testConnectionInternal()方法中会调用getLastPacketReceivedTimeMs()方法

testConnectionInternal()是用来检测连接是否有效的，在获取连接和归还连接时都有可能会调用该方法，这取决于Druid检测连接是否有效的参数

Druid检测连接是否有效的参数：

• testOnBorrow：每次获取连接时执行validationQuery检测连接是否有效（会影响性能）
• testOnReturn：每次归还连接时执行validationQuery检测连接是否有效（会影响性能）
• testWhileIdle：申请连接的时候检测，如果空闲时间大于timeBetweenEvictionRunsMillis，执行validationQuery检测连接是否有效
• 应用中设置了testOnBorrow=true，每次获取连接时，都会去抢占synchronized锁，所以性能下降的很明显

解决方案

经验证，使用Druid 1.x版本<=1.1.22会出现该bug，解决方案就是升级至Druid 1.x版本>=1.1.23或者Druid 1.2.x版本

GitHub issue：https://github.com/alibaba/druid/issues/3808

到此这篇关于低版本Druid连接池+MySQL驱动8.0导致线程阻塞、性能受限的文章就介绍到这了,更多相关MySQL驱动8.0低版本Druid连接池内容请搜索潘少俊衡以前的文章或继续浏览下面的相关文章希望大家以后多多支持潘少俊衡！