解决Flask-SQLAlchemy 2006 MySQL server has gone away 问题

配置信息

• python3 3.6
• Flask-SQLAlchemy 2.3.2
• win10

报错:

-----> [2018-07-16 17:22:42,041] [ERROR] [base.py<131>-base.run_job]: Job "auto_rollback..wrapper (trigger: interval[0:30:00], next run at: 2018-07-16 17:52:42 CST)" raised an exception
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1193, in _execute_context
    context)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 507, in do_execute
    cursor.execute(statement, parameters)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 250, in execute
    self.errorhandler(self, exc, value)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/connections.py", line 50, in defaulterrorhandler
    raise errorvalue
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 247, in execute
    res = self._query(query)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 411, in _query
    rowcount = self._do_query(q)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 374, in _do_query
    db.query(q)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/connections.py", line 277, in query
    _mysql.connection.query(self, query)
_mysql_exceptions.OperationalError: (2006, 'MySQL server has gone away')

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/apscheduler/executors/base.py", line 125, in run_job
    retval = job.func(*job.args, **job.kwargs)
  File "/home/zza/eth_crawler/crawler_script/utils.py", line 28, in wrapper
    raise err
  File "/home/zza/eth_crawler/crawler_script/utils.py", line 24, in wrapper
    return func(*args, **kwargs)
  File "/home/zza/eth_crawler/crawler_script/token_tracker.py", line 240, in update
    db_address = db.session.query(Token.contract_address).filter(None == Token.total_supply).all()
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2773, in all
    return list(self)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2925, in __iter__
    return self._execute_and_instances(context)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2948, in _execute_and_instances
    result = conn.execute(querycontext.statement, self._params)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 948, in execute
    return meth(self, multiparams, params)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/sql/elements.py", line 269, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1060, in _execute_clauseelement
    compiled_sql, distilled_params
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1200, in _execute_context
    context)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1413, in _handle_dbapi_exception
    exc_info
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 186, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1193, in _execute_context
    context)
  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 507, in do_execute
    cursor.execute(statement, parameters)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 250, in execute
    self.errorhandler(self, exc, value)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/connections.py", line 50, in defaulterrorhandler
    raise errorvalue
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 247, in execute
    res = self._query(query)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 411, in _query
    rowcount = self._do_query(q)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/cursors.py", line 374, in _do_query
    db.query(q)
  File "/usr/local/lib/python3.6/site-packages/MySQLdb/connections.py", line 277, in query
    _mysql.connection.query(self, query)
sqlalchemy.exc.OperationalError: (_mysql_exceptions.OperationalError) (2006, 'MySQL server has gone away') [SQL: 'SELECT token.contract_address AS token_contract_address \nFROM token \nWHERE token.total_supply IS NULL'] (Background on this error at: http://sqlalche.me/e/e3q8)

---

已使用解决方案

• 出错后需要rollback，为了后续程序能运行，给每个涉及sql语句的函数用了装饰器。

def auto_rollback(func):
    def wrapper(*args, **kwargs):
        try:
            return func(*args, **kwargs)
        except Exception as err:
            db.session.rollback()
            log.error(err)
            raise err

    return wrapper

治标不治本系列

• 把SQLALCHEMY_POOL_RECYCLE设成一个较小的数

app.config['SQLALCHEMY_POOL_SIZE'] = 128  # 线程池大小
app.config['SQLALCHEMY_POOL_TIMEOUT'] = 90  # 超时时间
app.config['SQLALCHEMY_POOL_RECYCLE'] = 3  # 空闲连接自动回收时间
app.config['SQLALCHEMY_MAX_OVERFLOW'] = 128  # 控制在连接池达到最大值后可以创建的连接数。

• 根据错误日志 在需要用数据库的地方先断开连接

db.session.remove()

失败

• 将单独的sql语句改成nopool连接方式

class nullpool_SQLAlchemy(SQLAlchemy):
    def apply_driver_hacks(self, app, info, options):
        super(nullpool_SQLAlchemy, self).apply_driver_hacks(app, info, options)
        from sqlalchemy.pool import NullPool
        options['poolclass'] = NullPool
        del options['pool_size']

解决后又会出现

sqlalchemy.exc.InvalidRequestError: Can't reconnect until invalid transaction is rolled back

失败

• 每次访问数据库重新生成sqlalchemy连接 ✔

    from xxx import SQLAlchemy
    from xxx import app
    db = SQLAlchemy(app)

最粗暴但是最有效的解决方式，这个问题困扰了将近3周，emmm

image.png

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解决参考

flask-alchemy mysql gone away问题 连接重连 程序方向
MySQL server has gone away 问题的解决方法 mysql反向
nullpool_SQLAlchemy代码
数据库方向解决问题