python mysql 断连报错处理

在使用python 对wordpress tag 进行细化代码处理时，遇到了调用MySQLdb模块时的出错，由于错误提示和问题原因相差甚远，查看了N久代码也未发现代码有问题。后来问了下师傅，被告知MySQLdb里有一个断接的坑 ，需要进行数据库重连解决。

一、报错代码及提示

运行出错的代码如下：

import MySQLdb
def getTerm(db,tag):
        cursor = db.cursor()
        query = "SELECT term_id FROM wp_terms where name=%s "
        count = cursor.execute(query,tag)
        rows = cursor.fetchall()
        db.commit()
        #db.close()
        if count:
                term_id = [int(rows[id][0]) for id in range(count)]
                return term_id
        else:return None
def addTerm(db,tag):
        cursor = db.cursor()
        query = "INSERT into wp_terms (name,slug,term_group) values (%s,%s,0)"
        data = (tag,tag)
        cursor.execute(query,data)
        db.commit()
        term_id = cursor.lastrowid
        sql = "INSERT into wp_term_taxonomy (term_id,taxonomy,description) values (%s,'post_tag',%s) "
        value = (term_id,tag)
        cursor.execute(sql,value)
        db.commit()
        db.close()
        return int(term_id)
dbconn = MySQLdb.connect(host='localhost', user='root', passwd='123456', db='361way', port=3306, charset='utf8', init_command='set names utf8')
tags = ['mysql','1111','aaaa','bbbb','ccccc','php','abc','python','java']
tagids = []
for tag in tags:
        termid = getTerm(dbconn,tag)
        if termid:
                print tag, 'tag id is ',termid
                tagids.extend(termid)
        else:
                termid = addTerm(dbconn,tag)
                print 'add tag',tag,'id is ' ,termid
                tagids.append(termid)
print 'tag id is ',tagids

直接可以执行，在第for循环里第二次调用getTerm函数时，报错如下：

Traceback (most recent call last):
  File "a.py", line 40, in <module>
    termid = getTerm(dbconn,tag)
  File "a.py", line 11, in getTerm
    count = cursor.execute(query,tag)
  File "/usr/lib64/python2.6/site-packages/MySQLdb/cursors.py", line 154, in execute
    charset = db.character_set_name()
_mysql_exceptions.InterfaceError: (0, '')

二、解决方法

初始时以为是编码问题了，又细核对了几遍未发现编码有问题，在python代码里也未发现异常。后来问过师傅后，师傅来了句提示：

只看代码有啥用，mysql 的超时时间调长点或捕获异常从连，原因是cursor. connection 没有关闭，但是socket已经断了cursor 这个行为不会再建立一次socket的重新执行一次MysqlDB.connect()

看的有点懵懂，先从mysql 里查看了所有timeout相关的变量

mysql> show GLOBAL VARIABLES like "%timeout%";
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| connect_timeout            | 10    |
| delayed_insert_timeout     | 300   |
| innodb_lock_wait_timeout   | 50    |
| innodb_rollback_on_timeout | OFF   |
| interactive_timeout        | 28800 |
| net_read_timeout           | 30    |
| net_write_timeout          | 60    |
| slave_net_timeout          | 3600  |
| table_lock_wait_timeout    | 50    |
| wait_timeout               | 28800 |
+----------------------------+-------+
10 rows in set (0.00 sec)

发现最小的超时时间是10s ，而我的程序执行起来显然就不了10s 。因为之前查过相关的报错，这里估计这个很可能是另外一个报错：2006，MySQL server has gone away  。即然和这个超时时间应该没关系，那就尝试通过MySQLdb ping测试，如果捕获异常，就再进行重连，修改后的代码为：

#!/usr/bin/python
#coding=utf-8
import MySQLdb
def getTerm(db,tag):
    cursor = db.cursor()
    query = "SELECT term_id FROM wp_terms where name=%s "
    count = cursor.execute(query,tag)
    rows = cursor.fetchall()
    db.commit()
    #db.close()
    if count:
        term_id = [int(rows[id][0]) for id in range(count)]
        print term_id
        return term_id
    else:return None
def addTerm(db,tag):
    cursor = db.cursor()
    query = "INSERT into wp_terms (name,slug,term_group) values (%s,%s,0)"
    data = (tag,tag)
    cursor.execute(query,data)
    db.commit()
    term_id = cursor.lastrowid
    sql = "INSERT into wp_term_taxonomy (term_id,taxonomy,description) values (%s,'post_tag',%s) "
    value = (term_id,tag)
    cursor.execute(sql,value)
    db.commit()
    db.close()
    return int(term_id)
dbconn = MySQLdb.connect(host='localhost', user='root', passwd='123456', db='361way', port=3306, charset='utf8', init_command='set names utf8')
tags = ['mysql','1111','aaaa','bbbb','ccccc','php','abc','python','java']
if __name__ == "__main__":
    tagids = []
    for tag in tags:
        try:
           dbconn.ping()
        except:
            print 'mysql connect have been close'
           dbconn = MySQLdb.connect(host='localhost', user='root', passwd='123456', db='361way', port=3306, charset='utf8', init_command='set names utf8')
        termid = getTerm(dbconn,tag)
        if termid:
            print tag, 'tag id is ',termid
            tagids.extend(termid)
        else:
            termid = addTerm(dbconn,tag)
            print 'add tag',tag,'id is ' ,termid
            tagids.append(termid)
    print 'All tags id is ',tagids

再执行发现竟然OK了，而细看下结果，发现基本上每1－2次getTerm或addTerm函数调用就会打印一次mysql connect have been close 。这里问题虽然已经解决，不过并未细挖到真正的根因。

三、建议

从网上要看的结果来看MySQLdb还有不支持长连接的坑，这个可以通过上面提到的修改my.cnf参数解决，也可以考虑使用其他支持设置timeout时间mysql模块。另外，也建议使用MySQLdb时，可以考虑使用一个对其二次封装的模块torndb —- A lightweight wrapper around MySQLdb 。

具体使用可以参看：http://tornado.readthedocs.org/en/branch2.4/database.html