Python/Django 脚本因 MySQL 死锁而崩溃

Question

以下脚本因死锁而出现错误:

sqlQuery = """INSERT INTO gps_points (gps_track_segment_id, gps_unit_id, date, lat,  lng) SELECT MAX(gps_track_segments.id) AS gps_track_segment_id, %(gps_unit_id)s AS gps_unit_id, %(date)s AS date, %(lat)s AS lat, %(lng)s AS lng FROM gps_track_segments 
    INNER JOIN gps_tracks ON gps_track_segments.gps_track_id = gps_tracks.id WHERE gps_tracks.hash = %(track)s"""

from django.db import connection, transaction
cursor = connection.cursor()
success = cursor.execute(sqlQuery, point)
transaction.commit_unless_managed()

错误日志显示:

2012-08-28 12:37:58,051 - django.db.backends - DEBUG - (0.018) INSERT INTO gps_points (gps_track_segment_id, gps_unit_id, date, lat, lng) SELECT MAX(gps_track_segments.id) AS gps_track_segment_id, 121 AS gps_unit_id, '2012-08-28 12:37:56' AS date, 51361100 AS lat, 4983910 AS lng FROM gps_track_segments 
    INNER JOIN gps_tracks ON gps_track_segments.gps_track_id = gps_tracks.id WHERE gps_tracks.hash = '7f5d950564786e182e175fb5d8e1b937528f85cc1ddabbee0d53859fb603ede3'; args={'gps_unit_id': 121L, 'lat': 51361100, 'date': '2012-08-28 12:37:56', 'course': None, 'track': u'7f5d950564786e182e175fb5d8e1b937528f85cc1ddabbee0d53859fb603ede3', 'speed': '0.0', 'lng': 4983910, 'segment': 5, 'altitude': None, 'accuracy': None}
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib64/python2.6/threading.py", line 532, in __bootstrap_inner
self.run()
  File "/usr/lib64/python2.6/threading.py", line 484, in run
self.__target(*self.__args, **self.__kwargs)
  ...
  ...
  File "/tcpserver/gpslibs.py", line 75, in saveGpsPoint
success = cursor.execute(sqlQuery, point)
  File "/usr/lib/python2.6/site-packages/django/db/backends/util.py", line 40, in execute
return self.cursor.execute(sql, params)
  File "/usr/lib/python2.6/site-packages/django/db/backends/mysql/base.py", line 114, in execute
return self.cursor.execute(query, args)
  File "/usr/lib64/python2.6/site-packages/MySQLdb/cursors.py", line 173, in execute
self.errorhandler(self, exc, value)
  File "/usr/lib64/python2.6/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
raise errorclass, errorvalue
DatabaseError: (1213, 'Deadlock found when trying to get lock; try restarting transaction')

使用mysql命令SHOW ENGINE INNODB STATUS我看到上面的查询与php网站请求的查询冲突。问题是有时 php-request 会回滚，有时会回滚 INSERT。最后一种情况会导致脚本因死锁错误而停止。 因为更改所涉及的查询非常困难。我现在喜欢如果:

我可以以某种方式制作一个不会因死锁而失败并再次尝试的 Django/Python 脚本吗？当然，我并不真正关心 php 请求失败或回滚。从可用性的角度来看，很容易处理这个问题。我确实关心后端脚本失败。这需要高于一切

Answer 1

Can I somehow make a Django/Python script that doesn't fail on the deadlock and just tries again?

您可以捕获引发的异常DatabaseError，然后再次执行事务的逻辑(也许通过在插入行之前先获取表上的写锁)。

try:
    success = cursor.execute(sqlQuery, point)
except DatabaseError:
     # retry here

理想情况下，您应该将其包装在可以再次调用的方法中。