springboot druid 數據庫連接池連接失敗后一直重連

在使用個人阿里雲測試機，在查詢實時輸出日志時，看到數據庫連接失敗后，服務器一直在重連服務器。開始以為是遭受重復攻擊，后面把服務重啟后，就沒有出現一直重連的情況。看以下輸出日志：

2022-02-09 11:04:58.896 ERROR 16876 --- [eate-1550991149] com.alibaba.druid.pool.DruidDataSource   : create connection SQLException, url: jdbc:mysql://47.98.67,98:1234/test?useSSL=false&characterEncoding=UTF-8&serverTimezone=UTC, errorCode 1045, state 28000

java.sql.SQLException: Access denied for user 'root'@'113.90.123.76' (using password: YES)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) ~[mysql-connector-java-8.0.16.jar:8.0.16]
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.16.jar:8.0.16]
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.16.jar:8.0.16]
	at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:835) ~[mysql-connector-java-8.0.16.jar:8.0.16]
	at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455) ~[mysql-connector-java-8.0.16.jar:8.0.16]
	at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240) ~[mysql-connector-java-8.0.16.jar:8.0.16]
	at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199) ~[mysql-connector-java-8.0.16.jar:8.0.16]
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:156) ~[druid-1.1.10.jar:1.1.10]
	at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:218) ~[druid-1.1.10.jar:1.1.10]
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:150) ~[druid-1.1.10.jar:1.1.10]
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1560) ~[druid-1.1.10.jar:1.1.10]
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1623) ~[druid-1.1.10.jar:1.1.10]
	at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2468) ~[druid-1.1.10.jar:1.1.10]

注意上面一直有 druid 數據庫連接池的提示，這里就想到可能是 druid 連接池的問題，然后去掉 druid maven 依賴后在請求接口就不會出現重連的問題。

druid 重連原因

在上圖源碼找到最后一行 DruidDataSource.java:2468 定位到源碼上，CreateConnectionThread 創建連接線程，看一下 CreateConnectionThread 源碼：

public class CreateConnectionThread extends Thread {

        public CreateConnectionThread(String name){
            super(name);
            this.setDaemon(true);
        }

        public void run() {
            initedLatch.countDown();

            long lastDiscardCount = 0;
            int errorCount = 0;
            for (;;) {
                // addLast
                try {
                    lock.lockInterruptibly();
                } catch (InterruptedException e2) {
                    break;
                }

                long discardCount = DruidDataSource.this.discardCount;
                boolean discardChanged = discardCount - lastDiscardCount > 0;
                lastDiscardCount = discardCount;

                try {
                    boolean emptyWait = true;

                    if (createError != null
                            && poolingCount == 0
                            && !discardChanged) {
                        emptyWait = false;
                    }

                    if (emptyWait
                            && asyncInit && createCount < initialSize) {
                        emptyWait = false;
                    }

                    if (emptyWait) {
                        // 必須存在線程等待，才創建連接
                        if (poolingCount >= notEmptyWaitThreadCount //
                                && !(keepAlive && activeCount + poolingCount < minIdle)) {
                            empty.await();
                        }

                        // 防止創建超過maxActive數量的連接
                        if (activeCount + poolingCount >= maxActive) {
                            empty.await();
                            continue;
                        }
                    }

                } catch (InterruptedException e) {
                    lastCreateError = e;
                    lastErrorTimeMillis = System.currentTimeMillis();

                    if (!closing) {
                        LOG.error("create connection Thread Interrupted, url: " + jdbcUrl, e);
                    }
                    break;
                } finally {
                    lock.unlock();
                }

                PhysicalConnectionInfo connection = null;

                try {
                    connection = createPhysicalConnection();
                    setFailContinuous(false);
                } catch (SQLException e) {
                    LOG.error("create connection SQLException, url: " + jdbcUrl + ", errorCode " + e.getErrorCode()
                              + ", state " + e.getSQLState(), e);

                    errorCount++;
                    if (errorCount > connectionErrorRetryAttempts && timeBetweenConnectErrorMillis > 0) {
                        // fail over retry attempts
                        setFailContinuous(true);
                        if (failFast) {
                            lock.lock();
                            try {
                                notEmpty.signalAll();
                            } finally {
                                lock.unlock();
                            }
                        }

                        if (breakAfterAcquireFailure) {
                            break;
                        }

                        try {
                            Thread.sleep(timeBetweenConnectErrorMillis);
                        } catch (InterruptedException interruptEx) {
                            break;
                        }
                    }
                } catch (RuntimeException e) {
                    LOG.error("create connection RuntimeException", e);
                    setFailContinuous(true);
                    continue;
                } catch (Error e) {
                    LOG.error("create connection Error", e);
                    setFailContinuous(true);
                    break;
                }

                if (connection == null) {
                    continue;
                }

                boolean result = put(connection);
                if (!result) {
                    JdbcUtils.close(connection.getPhysicalConnection());
                    LOG.info("put physical connection to pool failed.");
                }

                errorCount = 0; // reset errorCount
            }
        }
    }

這是一個多線程的類，而 run 方法里面設置了沒有限制的 for 循環 for (;;) {}, 而日志報錯定位的信息:

connection = createPhysicalConnection();

如果符合條件 errorCount > connectionErrorRetryAttempts && timeBetweenConnectErrorMillis > 0 會再次嘗試重連，先看一下這幾個參數的含義：

errorCount 錯誤次數

在 run 方法初始化時為零，每次連接失敗，會自動加1

connectionErrorRetryAttempts

連接錯誤重試次數，默認值為 1。

protected int  connectionErrorRetryAttempts  = 1;

timeBetweenConnectErrorMillis

連接間隔時間，單位毫秒。默認值為 500。

protected volatile long timeBetweenConnectErrorMillis = DEFAULT_TIME_BETWEEN_CONNECT_ERROR_MILLIS;
public static final long DEFAULT_TIME_BETWEEN_CONNECT_ERROR_MILLIS = 500;

我們在連接數據庫失敗后，要不在里面 break 中斷，其中有

if (breakAfterAcquireFailure) {
     break;
}

將改 break-after-acquire-failure 設置成 true,在 application.properties 文件如下配置：

spring.datasource.druid.break-after-acquire-failure=true

如果想多嘗試連接幾次，需要設置 connection-error-retry-attempts ,當 errorCount 大於 connectionErrorRetryAttempts 才會進入到 條件內，才會中斷循環。在 application.properties 文件如下配置：

spring.datasource.druid.connection-error-retry-attempts=3

總結

druid 數據庫連接失敗，是因為在使用多線程連接數據時使用了無限制循環連接，需要在連接失敗中斷連接，需要設置 break-after-acquire-failure 為 true。設置之后數據庫連接不成功也不會不斷的重試。如果要設置重連次數要設置 connection-error-retry-attempts。
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