别再乱升级 MySQL 驱动了。。
来源:https://blog.csdn.net/qq_4037...
现象
最近同事发现新服务用的驱动都是 MySQL8.0,而一些老系统 MySQL 驱动版本较低,存在一些危险漏洞,于是主动的把一些老应用的 MySQL 驱动程序升级到了 8.0。
然而升级后,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。
本文详细的分析了这次“破案”的全过程。
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)
通过上面的信息得知,有线程 BLOCKED 了,BLOCKED 的位置在 com.alibaba.druid.util.Utils.loadClass(Utils.java:220),于是重点的查看这一块的代码,最终发现了问题。
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
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/dr...
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