目錄
- 現象
- 根因分析
- getLastPacketReceivedTimeMs()方法調用時機
- 解決方案
現象
應用升級MySQL驅動8.0后，在并發量較高時，查看監控打點，Druid連接池拿到連接并執行SQL的時間大部分都超過200ms
對系統進行壓測，發現出現大量線程阻塞的情況，線程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()方法會加載com.mysql.jdbc.MySQLConnection這個類，但在MySQL驅動8.0中類名改為com.mysql.cj.jdbc.ConnectionImpl，所以MySQL驅動8.0中加載不到com.mysql.jdbc.MySQLConnection
getLastPacketReceivedTimeMs()方法實現中，如果Utils.loadClass("com.mysql.jdbc.MySQLConnection")加載不到類并拋出異常，會修改變量class_connectionImpl_Error，下次調用不會再進行加載
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()方法中同樣catch了ClassNotFoundException，這就導致loadClass()在加載不到類的時候，并不會拋出異常，從而會導致每調用一次getLastPacketReceivedTimeMs()方法，就會加載一次MySQLConnection這個類
線程dump信息中可以看到是在調用TomcatEmbeddedWebappClassLoader的loadClass()方法時，導致線程阻塞的
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);
}
}
這是因為TomcatEmbeddedWebappClassLoader在加載類的時候，會加synchronized鎖，這就導致每調用一次getLastPacketReceivedTimeMs()方法，就會加載一次com.mysql.jdbc.MySQLConnection，而又始終加載不到，在加載類的時候會加synchronized鎖，所以會出現線程阻塞，性能下降的現象
getLastPacketReceivedTimeMs()方法調用時機
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()方法中會調用getLastPacketReceivedTimeMs()方法
testConnectionInternal()是用來檢測連接是否有效的，在獲取連接和歸還連接時都有可能會調用該方法，這取決于Druid檢測連接是否有效的參數
Druid檢測連接是否有效的參數：
- testOnBorrow：每次獲取連接時執行validationQuery檢測連接是否有效（會影響性能）
- testOnReturn：每次歸還連接時執行validationQuery檢測連接是否有效（會影響性能）
- testWhileIdle：申請連接的時候檢測，如果空閑時間大于timeBetweenEvictionRunsMillis，執行validationQuery檢測連接是否有效
- 應用中設置了testOnBorrow=true，每次獲取連接時，都會去搶占synchronized鎖，所以性能下降的很明顯
解決方案
經驗證，使用Druid 1.x版本=1.1.22會出現該bug，解決方案就是升級至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
到此這篇關于低版本Druid連接池+MySQL驅動8.0導致線程阻塞、性能受限的文章就介紹到這了,更多相關MySQL驅動8.0低版本Druid連接池內容請搜索腳本之家以前的文章或繼續瀏覽下面的相關文章希望大家以后多多支持腳本之家！
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