优雅地处理“MySQL已经消失”

我正在Python中编写一个小型的数据库适配器，主要是为了好玩。我试图让代码从MySQL连接“消失”的情况中正常恢复，也就是wait_timeout被超出。我已经设置wait_timeout在10，所以我可以试试这个。优雅地处理“MySQL已经消失”

这里是我的代码：

def select(self, query, params=[]): 
     try: 
      self.cursor = self.cxn.cursor() 
      self.cursor.execute(query, params) 
     except MySQLdb.OperationalError, e: 
      if e[0] == 2006: 
       print "We caught the exception properly!" 
       print self.cxn 
       self.cxn.close() 
       self.cxn = self.db._get_cxn() 
       self.cursor = self.cxn.cursor() 
       self.cursor.execute(query, params) 
       print self.cxn 

     return self.cursor.fetchall()

接下来，我等待10秒钟，并尝试提出请求。以下是CherryPy的外观：

[31/Dec/2009:20:47:29] ENGINE Bus STARTING 
[31/Dec/2009:20:47:29] ENGINE Starting database pool... 
[31/Dec/2009:20:47:29] ENGINE POOL Connecting to MySQL... 
[31/Dec/2009:20:47:29] ENGINE POOL Connecting to MySQL... 
[31/Dec/2009:20:47:29] ENGINE POOL Connecting to MySQL... 
[31/Dec/2009:20:47:29] ENGINE POOL Connecting to MySQL... 
[31/Dec/2009:20:47:29] ENGINE POOL Connecting to MySQL... 
[31/Dec/2009:20:47:29] ENGINE Started monitor thread '_TimeoutMonitor'. 
[31/Dec/2009:20:47:29] ENGINE Started monitor thread 'Autoreloader'. 
[31/Dec/2009:20:47:30] ENGINE Serving on 0.0.0.0:8888 
[31/Dec/2009:20:47:30] ENGINE Bus STARTED 
We caught the exception properly! <====================================== Aaarg! 
<_mysql.connection open to 'localhost' at 1ee22b0> 
[31/Dec/2009:20:48:25] HTTP Traceback (most recent call last): 
    File "/usr/local/lib/python2.6/dist-packages/CherryPy-3.1.2-py2.6.egg/cherrypy/_cprequest.py", line 606, in respond 
cherrypy.response.body = self.handler() 
    File "/usr/local/lib/python2.6/dist-packages/CherryPy-3.1.2-py2.6.egg/cherrypy/_cpdispatch.py", line 25, in __call__ 
    return self.callable(*self.args, **self.kwargs) 
    File "adp.py", line 69, in reports 
    page.sources = sql.GetSources() 
    File "/home/swoods/dev/adp/sql.py", line 45, in __call__ 
    return getattr(self.formatter.cxn, parsefn)(sql, sql_vars) 
    File "/home/swoods/dev/adp/database.py", line 96, in select 
    self.cursor.execute(query, params) 
    File "/usr/lib/pymodules/python2.6/MySQLdb/cursors.py", line 166, in execute 
    self.errorhandler(self, exc, value) 
    File "/usr/lib/pymodules/python2.6/MySQLdb/connections.py", line 35, in defaulterrorhandler 
    raise errorclass, errorvalue 
OperationalError: (2006, 'MySQL server has gone away') 

[31/Dec/2009:20:48:25] HTTP 
Request Headers: 
    COOKIE: session_id=e14f63acc306b26f14d966e606612642af2dd423 
    HOST: localhost:8888 
    CACHE-CONTROL: max-age=0 
    ACCEPT: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 
    ACCEPT-CHARSET: ISO-8859-1,utf-8;q=0.7,*;q=0.3 
    USER-AGENT: Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/532.5 (KHTML, like  Gecko) Chrome/4.0.249.43 Safari/532.5 
    CONNECTION: keep-alive 
    Remote-Addr: 127.0.0.1 
    ACCEPT-LANGUAGE: en-US,en;q=0.8 
    ACCEPT-ENCODING: gzip,deflate 
127.0.0.1 - - [31/Dec/2009:20:48:25] "GET /reports/1 HTTP/1.1" 500 1770 "" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/532.5 (KHTML, like Gecko) Chrome/4.0.249.43 Safari/532.5"

为什么不工作？我清楚地捕捉到异常，重新生成连接和光标，但它仍然不起作用。它与MySQLdb如何获得连接有关？

来源

2010-01-01 Sean Woods

从代码中看不到，但我的猜测是db._get_cxn()方法正在做某种连接池并返回现有连接对象而不是创建新连接对象。是否没有打电话给db来冲洗现有的无用连接？（你应该真的打电话给一个内部的_ - 前缀的方法？）

为了防止MySQL has gone away我通常更喜欢保留一个时间戳与我最后一次使用它的连接。然后再尝试再次使用它，我看看时间戳，并关闭/放弃连接，如果它是最近几个小时以前使用的。这节省了用try...except OperationalError...try again包装每一个可能的查询。

来源

2010-01-01 02:46:49 bobince

正确的你是在这两个帐户。这件事已经走向了许多不同的方向。我实际上实施了第2段的建议，这是我喜欢的做事方式。我已经重写了代码来修复你在第一段中提出的错误（错误就是这样的......我是我自己重构的受害者）。非常感谢您的帮助。新年快乐！ – 2010-01-01 05:33:27

@SeanWoods - 你能分享一下你正确的代码吗？我遭受同样的问题，你做... – Jonathan 2011-10-20 09:56:29

@SeanWoods你有没有想过分享代码的任何想法？看起来我也遭受同样的错误。我已经在我的初始数据库连接周围放了一个while循环来进行3次尝试，但正如bobince所提到的，除了每个查询之外，我都试过了。我确实尝试除了每一个查询，但我没有真正捕捉到服务器发生异常。 – 2013-03-23 16:25:32

优雅地处理“MySQL已经消失”

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