先说一个事实:Django ORM 数据库连接模式是:每个 request 独立的数据库连接。
就是 Django 每一个 request 都会创建一个数据库连接,并且在 response 之后,关闭数据库连接。每一个 request 的数据库连接都是独立的!
众所周知,出于节约资源的考虑,客户端在一段时间没有动作之后,服务端会主动关闭连接,此时如果我们继续使用已经被服务器关闭的连接会报什么错误呢?
当访问数据库,但是服务端已经主动关闭连接了,此时会报什么错误?
错误类型
mysql
客户端对数据库进行操作时,打开终端窗口,如果一段时间没有操作,再次操作时,常常会报如下错误:
ERROR 2013 (HY000): Lost connection to MySQL server during query
ERROR 2006 (HY000): MySQL server has gone away No connection. Trying to reconnect...
好的,让我们看看这两个错误对应 pymysql
中的异常类型吧
2013 错误码对应的是什么异常类型?
先看第一个 2013
对应的异常类型constants/CR.py
CR_SERVER_LOST = 2013
connections.py
raise err.OperationalError(
CR.CR_SERVER_LOST,
"Lost connection to MySQL server during query",
)
可以看到对应的错误类型是 OperationalError
2006 错误码对应的是什么异常类型?
再看第二个 2006
对应的异常类型constants/CR.py
CR_SERVER_GONE_ERROR = 2006
connections.py
raise err.OperationalError(
CR.CR_SERVER_GONE_ERROR, "MySQL server has gone away (%r)" % (e,)
)
可以看到对应的错误类型是 OperationalError
operational 是什么意思?
看看 有道翻译 中的解释吧
operational
英 [ˌɒpəˈreɪʃənl] 美 [ˌɑːpəˈreɪʃənl]
adj. (机器、设备等)正常运转的,可使用的;操作的,运营的,业务的;军事行动的;操作论的,操作主义的
从这个翻译来看,这个异常类是一个很宽泛的异常类
动手做一做
实验环境如下所示:
(twitter) ╭─bot@mbp13m1.local ~/Desktop/code/python/twitter ‹main*›
╰─➤ python --version
Python 3.9.7
(twitter) ╭─bot@mbp13m1.local ~/Desktop/code/python/twitter ‹main*›
╰─➤ pip show django
Name: Django
Version: 3.2.9
Summary: A high-level Python Web framework that encourages rapid development and clean, pragmatic design.
Home-page: https://www.djangoproject.com/
Author: Django Software Foundation
Author-email: foundation@djangoproject.com
License: BSD-3-Clause
Location: /Users/bot/.local/share/virtualenvs/twitter-73pfN55g/lib/python3.9/site-packages
Requires: asgiref, pytz, sqlparse
Required-by: django-filter, django-oss-storage, djangorestframework
查看和修改默认的 time_out 参数
Mysql 主动关闭无动作的连接的阈值是变量 time_out
指定的。
使用如下语句查看该值:
show global variables like '%timeout%';
结果如下
mysql root@192.168.31.203:d_twitter_db> show global variables like '%timeout%';
+-----------------------------------+----------+
| Variable_name | Value |
+-----------------------------------+----------+
| connect_timeout | 10 |
| delayed_insert_timeout | 300 |
| have_statement_timeout | YES |
| innodb_flush_log_at_timeout | 1 |
| innodb_lock_wait_timeout | 50 |
| innodb_rollback_on_timeout | OFF |
| interactive_timeout | 28800 |
| lock_wait_timeout | 31536000 |
| mysqlx_connect_timeout | 30 |
| mysqlx_idle_worker_thread_timeout | 60 |
| mysqlx_interactive_timeout | 28800 |
| mysqlx_port_open_timeout | 0 |
| mysqlx_read_timeout | 30 |
| mysqlx_wait_timeout | 28800 |
| mysqlx_write_timeout | 60 |
| net_read_timeout | 30 |
| net_write_timeout | 60 |
| replica_net_timeout | 60 |
| rpl_stop_replica_timeout | 31536000 |
| rpl_stop_slave_timeout | 31536000 |
| slave_net_timeout | 60 |
| wait_timeout | 28800 |
+-----------------------------------+----------+
22 rows in set
Time: 0.028s
mysql root@192.168.31.203:d_twitter_db>
wait_timeout
:服务器关闭非交互连接之前等待活动的秒数,就是你在你的项目中进行程序调用
interactive_timeout
: 服务器关闭交互式连接前等待活动的秒数,就是你在你的本机上打开mysql的客户端,cmd的那种
如果要修改 time_out
的值,可以执行如下的语句:
set global wait_timeout=10;
方便看 Django 会抛出什么错误,就设为很短的 10 秒吧。
启动 Django ,然后先执行一次查询,(确保连接上数据库),然后等 10 秒后再重复执行一次
Django 什么时候会去连接数据库?
通过 Wireshark 抓包和观察会话管理,可以确认的是:python manage.py shell
的时候,不会去连接数据库,导入模型也不会去连接数据库,只有当进行真正的 CRUD 才会去连接数据库,且是长连接
如何查看会话管理:👇SELECT * FROM `information_schema`.`PROCESSLIST` P
Tweet.objects.all()
结果不出意外的报错了
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/pymysql/connections.py in _read_query_result(self, unbuffered)
773 else:
774 result = MySQLResult(self)
--> 775 result.read()
776 self._result = result
777 if result.server_status is not None:
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/pymysql/connections.py in read(self)
1154 def read(self):
1155 try:
-> 1156 first_packet = self.connection._read_packet()
1157
1158 if first_packet.is_ok_packet():
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/pymysql/connections.py in _read_packet(self, packet_type)
699 if packet_number == 0:
700 # MariaDB sends error packet with seqno==0 when shutdown
--> 701 raise err.OperationalError(
702 CR.CR_SERVER_LOST,
703 "Lost connection to MySQL server during query",
OperationalError: (2013, 'Lost connection to MySQL server during query')
再执行一次看看会不会重连。
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/django/db/backends/mysql/base.py in execute(self, query, args)
71 try:
72 # args is None means no string interpolation
---> 73 return self.cursor.execute(query, args)
74 except Database.OperationalError as e:
75 # Map some error codes to IntegrityError, since they seem to be
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/pymysql/cursors.py in execute(self, query, args)
146 query = self.mogrify(query, args)
147
--> 148 result = self._query(query)
149 self._executed = query
150 return result
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/pymysql/cursors.py in _query(self, q)
308 self._last_executed = q
309 self._clear_result()
--> 310 conn.query(q)
311 self._do_get_result()
312 return self.rowcount
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/pymysql/connections.py in query(self, sql, unbuffered)
545 if isinstance(sql, str):
546 sql = sql.encode(self.encoding, "surrogateescape")
--> 547 self._execute_command(COMMAND.COM_QUERY, sql)
548 self._affected_rows = self._read_query_result(unbuffered=unbuffered)
549 return self._affected_rows
~/.local/share/virtualenvs/twitter-jSQKCUr2/lib/python3.9/site-packages/pymysql/connections.py in _execute_command(self, command, sql)
791 """
792 if not self._sock:
--> 793 raise err.InterfaceError(0, "")
794
795 # If the last query was unbuffered, make sure it finishes before
InterfaceError: (0, '')
好吧,没有 Django 没有帮我们重连,只是报错类型不一样了。不管在执行多少次 Tweet.objects.all()
结果都是上面的 InterfaceError: (0, '')
解决方案 —— 重新建立连接
Django 提供了 close_old_connections
方法
from django.db import close_old_connections
from django.db.utils import OperationalError
def job(self):
try:
something()
except OperationalError as error:
self.logger.error(f'job error: {error}', exc_info=True)
close_old_connections()
except Exception as error:
self.logger.error(f'job error: {error}', exc_info=True)
参考文章:
MySQL中interactive_timeout和wait_timeout的区别
[玩转 MySQL 之二]MySQL 连接机制浅析及运维
MySQL数据库连接超时自动断开的解决方案
解决mysql服务器在无操作超时主动断开连接的情况
Mysql查看连接数(连接总数、活跃数、最大并发数)
PEP 249 -- Python Database API Specification v2.0
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