mysql> START TRANSACTION;Query OK, 0 rows affected (0.00 sec)mysql> SELECT * FROM blog WHERE id = 12 LOCK IN SHARE MODE;+----+-------+-----------+| id | name | author_id |+----+-------+-----------+| 12 | testA | 50 |+----+-------+-----------+1 row in set (0.00 sec)

mysql> START TRANSACTION;Query OK, 0 rows affected (0.00 sec)mysql> DELETE FROM blog WHERE id = 12;

mysql> DELETE FROM blog WHERE id = 12;Query OK, 1 row affected (0.00 sec)

<environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${jdbc.driver}"/><property name="url" value="${jdbc.url}"/><property name="username" value="${jdbc.username}"/><property name="password" value="${jdbc.password}"/></dataSource></environment> 當數據庫連接池的連接數用光了之后就要等2s再去獲取：while (conn == null) {synchronized (state) {if (!state.idleConnections.isEmpty()) {// Pool has available connectionconn = state.idleConnections.remove(0);if (log.isDebugEnabled()) {log.debug("Checked out connection " + conn.getRealHashCode() + " from pool.");}} else {// Pool does not have available connectionif (state.activeConnections.size() < poolMaximumActiveConnections) {// Can create new connectionconn = new PooledConnection(dataSource.getConnection(), this);if (log.isDebugEnabled()) {log.debug("Created connection " + conn.getRealHashCode() + ".");}} else {// Cannot create new connectionPooledConnection oldestActiveConnection = state.activeConnections.get(0);long longestCheckoutTime = oldestActiveConnection.getCheckoutTime();if (longestCheckoutTime > poolMaximumCheckoutTime) {// Can claim overdue connectionstate.claimedOverdueConnectionCount++;state.accumulatedCheckoutTimeOfOverdueConnections += longestCheckoutTime;state.accumulatedCheckoutTime += longestCheckoutTime;state.activeConnections.remove(oldestActiveConnection);if (!oldestActiveConnection.getRealConnection().getAutoCommit()) {try {oldestActiveConnection.getRealConnection().rollback();} catch (SQLException e) {log.debug("Bad connection. Could not roll back");} }conn = new PooledConnection(oldestActiveConnection.getRealConnection(), this);oldestActiveConnection.invalidate();if (log.isDebugEnabled()) {log.debug("Claimed overdue connection " + conn.getRealHashCode() + ".");}} else {// Must waittry {if (!countedWait) {state.hadToWaitCount++;countedWait = true;}if (log.isDebugEnabled()) {log.debug("Waiting as long as " + poolTimeToWait + " milliseconds for connection.");}long wt = System.currentTimeMillis();state.wait(poolTimeToWait);state.accumulatedWaitTime += System.currentTimeMillis() - wt;} catch (InterruptedException e) {break;}}}}if (conn != null) {if (conn.isValid()) {if (!conn.getRealConnection().getAutoCommit()) {conn.getRealConnection().rollback();}conn.setConnectionTypeCode(assembleConnectionTypeCode(dataSource.getUrl(), username, password));conn.setCheckoutTimestamp(System.currentTimeMillis());conn.setLastUsedTimestamp(System.currentTimeMillis());state.activeConnections.add(conn);state.requestCount++;state.accumulatedRequestTime += System.currentTimeMillis() - t;} else {if (log.isDebugEnabled()) {log.debug("A bad connection (" + conn.getRealHashCode() + ") was returned from the pool, getting another connection.");}state.badConnectionCount++;localBadConnectionCount++;conn = null;if (localBadConnectionCount > (poolMaximumIdleConnections + 3)) {if (log.isDebugEnabled()) {log.debug("PooledDataSource: Could not get a good connection to the database.");}throw new SQLException("PooledDataSource: Could not get a good connection to the database.");}}}}}