使用数据库连接池场景下的 too many connections 问题排查

// 通过指定数据源，执行对应的 update SQL
@PostMapping("/update/{dataSource}/{count}")
public ResponseResult<String> update(@PathVariable String dataSource, @PathVariable Integer count , @RequestBody String sql) {
    // 获取数据源
    Map<String, DataSource> dataSourceMap = getDataSources();
    DataSource source = dataSourceMap.get(dataSource);
    // 执行
    return ResponseResult.ok(sqlService.execute(source,sql,count));
}

/**
 * HikariDataSource Connection 会自动关闭 Statement
 * @see com.zaxxer.hikari.pool.ProxyConnection This is the proxy class for java.sql.Connection.
 */
@Override
public final void close() throws SQLException {
  // automatic resource cleanup
  closeStatements();

  if (delegate != ClosedConnection.CLOSED_CONNECTION) {
	 try {
		// fall back operation...
		if (isCommitStateDirty && !isAutoCommit) {
		   delegate.rollback();
		}
	 }
	 finally {
		// return resource
		delegate = ClosedConnection.CLOSED_CONNECTION;
		poolEntry.recycle(lastAccess);
	 }
  }
}

// 关闭 statement, 会级联关闭 results
// @see com.mysql.jdbc.StatementImpl#realClose
protected synchronized void realClose(boolean calledExplicitly, boolean closeOpenResults) throws SQLException {
	if (closeOpenResults) {
		if (this.results != null) {
			try {
				this.results.close();
			} catch (Exception var4) {
			}
		}
		this.closeAllOpenResults();
	}
}

/**
* We only create connections if we need another idle connection or have threads still waiting
* for a new connection.  Otherwise we bail out of the request to create.
*
* @return true if we should create a connection, false if the need has disappeared
* @see com.zaxxer.hikari.pool.HikariPool.PoolEntryCreator#shouldCreateAnotherConnection
*/
private synchronized boolean shouldCreateAnotherConnection() {
	// The property controls the maximum number of connections that HikariCP will keep in the pool, including both idle and in-use connections.
	return getTotalConnections() < config.getMaximumPoolSize() &&
	(connectionBag.getWaitingThreadCount() > 0 || getIdleConnections() < config.getMinimumIdle());
}

public Map<String, DataSource> getDataSources(){
	// 没有缓存或者单例处理，每调用一次，初始化一次 DataSource 😅
	Map<String, DataSource> dataSources = new HashMap<>();
	datadaSourcesConfig.forEach((k, v) -> {
		// spring boot, Convenience class for building a DataSource with common implementations and properties.
		DataSourceBuilder builder = DataSourceBuilder.create();
		builder.url(v.getUrl());
		builder.username(v.getUsername());
		builder.password(v.getPassword());
		DataSource dataSource = builder.build();
		dataSources.put(k, dataSource);
	});
	return dataSources;
}

// 启用自动连接，HighAvailability
private BooleanConnectionProperty autoReconnect = new BooleanConnectionProperty("autoReconnect", false, Messages.getString("ConnectionProperties.autoReconnect"), "1.1", HA_CATEGORY, 0);

// 最多尝试连接次数，默认 3 次。
private IntegerConnectionProperty maxReconnects = new IntegerConnectionProperty("maxReconnects", 3, 1, Integer.MAX_VALUE, Messages.getString("ConnectionProperties.maxReconnects"), "1.1", HA_CATEGORY, 4);

// 异常提示配置 mysql-connector-java-5.1.47.jar!\com\mysql\jdbc\LocalizedErrorMessages.properties
Connection.UnableToConnectWithRetries=Could not create connection to database server. \
Attempted reconnect {0} times. Giving up.

// autoReconnect 
public void createNewIO(boolean isForReconnect) throws SQLException {
    synchronized (getConnectionMutex()) {
        // jdbc.url autoReconnect 指定为 true，识别为 HighAvailability
        if (!getHighAvailability()) {
            connectOneTryOnly(isForReconnect, mergedProps);
            return;
        }
        // maxReconnects 默认为 3，重试失败的提示就是： Attempted reconnect 3 times. Giving up.
        connectWithRetries(isForReconnect, mergedProps);
    }
}