气流psycopg2.OperationalError：严重：对不起，已经有太多客户端

我有一个四节点集群的Airflow环境，对我来说，几个月来一直运行良好。

ec2实例

服务器1：Web服务器，调度程序，Redis队列，PostgreSQL数据库

服务器2：Web服务器

服务器3：工作者

服务器4：工作者

最近，我正在开发一个更复杂的DAG，其中包含数十个任务，而我之前从事的工作相对较小。我不确定这是否就是为什么我现在看到此错误弹出或者是什么原因，但是我偶尔会收到此错误：

在Airflow UI上，该任务的日志下：

psycopg2.OperationalError: FATAL: sorry, too many clients already

在Webserver上（运行airflow webserver的输出），我也得到了相同的错误：

[2018-07-23 17:43:46 -0400] [8116] [ERROR] Exception in worker process
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2158, in _wrap_pool_connect
    return fn()
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 403, in connect
    return _ConnectionFairy._checkout(self)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 788, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 532, in checkout
    rec = pool._do_get()
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1193, in _do_get
    self._dec_overflow()
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 187, in reraise
    raise value
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1190, in _do_get
    return self._create_connection()
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 350, in _create_connection
    return _ConnectionRecord(self)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 477, in __init__
    self.__connect(first_connect_check=True)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/pool.py", line 671, in __connect
    cOnnection= pool._invoke_creator(self)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/strategies.py", line 106, in connect
    return dialect.connect(*cargs, **cparams)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 410, in connect
    return self.dbapi.connect(*cargs, **cparams)
  File "/usr/local/lib64/python3.6/site-packages/psycopg2/__init__.py", line 130, in connect
    cOnn= _connect(dsn, connection_factory=connection_factory, **kwasync)
psycopg2.OperationalError: FATAL:  sorry, too many clients already

我可以通过运行sudo /etc/init.d/postgresql restart并重新启动DAG 来解决此问题，但是大约运行三遍后，我将再次开始看到错误。

我没有找到有关Airflow的任何细节，但是从其他类似的帖子中，我发现这是因为我的客户（在这种情况下，我是Airflow）正在尝试建立更多的连接到PostgreSQL，而不是配置为PostgreSQL处理的内容。我运行以下命令发现我的PostgreSQL可以接受100个连接：

[ec2-user@ip-1-2-3-4 ~]$ sudo su
root@ip-1-2-3-4
[/home/ec2-user]# psql -U postgres
psql (9.2.24)
Type "help" for help.

postgres=# show max_connections;
 max_connections
-----------------
 100
(1 row)

在此解决方案中，帖子说我可以增加PostgreSQL最大连接数，但是我想知道是否应该在Airflow.cfg文件中设置一个值，以便可以将Airflow允许的连接大小与PoastgreSQL最大连接大小匹配。有谁知道我可以在Airflow中设置此值？以下是我认为相关的字段：

# The SqlAlchemy pool size is the maximum number of database connections
# in the pool.
sql_alchemy_pool_size = 5

# The SqlAlchemy pool recycle is the number of seconds a connection
# can be idle in the pool before it is invalidated. This config does
# not apply to sqlite.
sql_alchemy_pool_recycle = 3600

# The amount of parallelism as a setting to the executor. This defines
# the max number of task instances that should run simultaneously
# on this airflow installation
parallelism = 32

# The number of task instances allowed to run concurrently by the scheduler
dag_cOncurrency= 32

# When not using pools, tasks are run in the "default pool",
# whose size is guided by this config element
non_pooled_task_slot_count = 128

# The maximum number of active DAG runs per DAG
max_active_runs_per_dag = 32

公开解决此问题的任何建议。这与我的Airflow配置有关还是PostgreSQL配置有问题？

另外，由于我正在测试新的DAG，因此有时会终止正在运行的任务并将其重新开始。也许这样做会导致某些进程无法正确终止，并使死连接保持对PostgreSQL的开放状态？