python - django 事务原子性..是信任吗？

Question

你见过我看代码吗？ 我正在使用 django 1.8、django-rest-framework、mysql/innodb。

我认为你总能得到不同的值(value)和回应。 但是...事实并非如此。

'01500701.20040128100031383','01500701.20040128100031262' <-- 像这样!!!

有时会响应其他地方的值。(其他，另一个客户端..worker1，worker2，worker3..) 我能知道为什么会发生这种情况吗？

[ View .py]

class NewsUrlList(mixins.ListModelMixin, mixins.CreateModelMixin, generics.GenericAPIView):
    def get(self, request, *args, **kwargs):

        abab = self.check_urlqueuesize()
        logger.debug("NewsUrlList Get Response id=[%s], data=[%s]", request.user.username, abab)
        return Response(abab, status=status.HTTP_200_OK)

    def post(self, request, *args, **kwargs):
        .. blsh blah..

...

@transaction.atomic
def check_urlqueuesize(self):
    if r.llen("url_list") < 5:  # <- redis list
        with transaction.atomic():
            readydata = NewsUrl.objects.filter(status='R')[:100]
            for a in readydata:
                r.rpush("url_list", a.link)  # <- redis list
                a.status = 'W'
                a.save(update_fields=['status'])

        responsjson = {}
        list1 = []

        for c in range(0, 7):
            list1.append(r.lpop("url_list").decode("utf-8"))

        responsjson["urls"] = list1
        return responsjson

[模型.py]

class NewsUrl(models.Model):
    link = models.CharField(max_length=100, primary_key=True)
    title = models.TextField(default='')
    publisher = models.CharField(max_length=150, blank=True, default='')
    status = models.CharField(max_length=1, default='R')  # R:Ready, W:Working, D:Done, E:Error
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)

[日志]

2015-12-10 15:42:42,941 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker3], data=[{'urls': ['01500701.20040128100031262', '01500701.20040128100031263', '01500701.20040128100031266', '01500701.20040128100031442', '01500701.20040128100031441', '01500701.20040128100031439', '01500701.20040128100031438'], 'size': 7}]
2015-12-10 15:42:54,639 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker2], data=[{'urls': ['01500701.20040128100031440', '01500701.20040128100031437', '01100201.20040128K1401.bak', '01100201.20040128K3602.bak', '01500701.20040128100031353', '01500701.20040128100031366', '01500701.20040128100031310'], 'size': 7}]
2015-12-10 15:42:57,148 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker3], data=[{'urls': ['01500701.20040128100031355', '01500701.20040128100031408', '01500701.20040128100031409', '01500701.20040128100031410', '01500701.20040128100031309', '01500701.20040128100031271', '01500701.20040128100031411'], 'size': 7}]
2015-12-10 15:42:57,555 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker1], data=[{'urls': ['01500701.20040128100031401', '01500701.20040128100031417', '01500701.20040128100031434', '01500701.20040128100031435', '01500701.20040128100031394', '01500701.20040128100031368', '01500701.20040128100031278'], 'size': 7}]
2015-12-10 15:43:08,069 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker2], data=[{'urls': ['01500701.20040128100031367', '01500701.20040128100031369', '01500701.20040128100031373', '01500701.20040128100031414', '01500701.20040128100031358', '01500701.20040128100031428', '01500701.20040128100031381'], 'size': 7}]
2015-12-10 15:43:09,262 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker3], data=[{'urls': ['01500701.20040128100031376', '01500701.20040128100031271', '01500701.20040128100031356', '01500701.20040128100031400', '01500701.20040128100031398', '01500701.20040128100031399', '01500701.20040128100031430'], 'size': 7}]
2015-12-10 15:43:09,731 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker1], data=[{'urls': ['01500701.20040128100031431', '01500701.20040128100031433', '01500701.20040128100031429', '01500701.20040128100031432', '01500701.20040128100031421', '01500701.20040128100031420', '01500701.20040128100031427'], 'size': 7}]
2015-12-10 15:43:24,308 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker3], data=[{'urls': ['01500701.20040128100031454', '01500701.20040128100031453', '01500701.20040128100031276', '01500701.20040128100031251', '01500701.20040128100031252', '01500701.20040128100031451', '01500701.20040128100031452'], 'size': 7}]
2015-12-10 15:43:24,686 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker1], data=[{'urls': ['01500701.20040128100031271', '01500701.20040128100031270', '01500701.20040128100031272', '01500701.20040128100031254', '01500701.20040128100031456', '01500701.20040128100031255', '01500701.20040128100031256'], 'size': 7}]
2015-12-10 15:43:33,765 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker2], data=[{'urls': ['01500701.20040128100031257', '01500701.20040128100031262', '01500701.20040128100031260', '01100401.20040226D1901.bak', '01100201.20040226K0401.bak', '01500701.20040226100036237', '01500701.20040127100031057'], 'size': 7}]
2015-12-10 15:43:40,245 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker1], data=[{'urls': ['01500701.20040127100031150', '01500701.20040127100031059', '01500701.20040127100031149', '01500701.20040127100031248', '01500701.20040127100031249', '01500701.20040127100031247', '01500701.20040127100031058'], 'size': 7}]
2015-12-10 15:43:41,202 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker3], data=[{'urls': ['01500701.20040127100031216', '01500701.20040127100031119', '01500701.20040127100031123', '01500701.20040127100031120', '01500701.20040127100031113', '01500701.20040127100031115', '01500701.20040127100031117'], 'size': 7}]
2015-12-10 15:43:46,030 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker2], data=[{'urls': ['01500701.20040127100031118', '01500701.20040127100031116', '01500701.20040127100031121', '01500701.20040127100031151', '01500701.20040127100031152', '01500701.20040127100031158', '01500701.20040127100031155'], 'size': 7}]
2015-12-10 15:43:52,295 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker1], data=[{'urls': ['01500701.20040128100031262', '01500701.20040127100031157', '01500701.20040127100031153', '01500701.20040127100031154', '01500701.20040127100031162', '01500701.20040127100031122', '01500701.20040127100031075'], 'size': 7}]
2015-12-10 15:43:53,130 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker3], data=[{'urls': ['01500701.20040127100031076', '01500701.20040127100031183', '01500701.20040127100031185', '01500701.20040127100031056', '01500701.20040127100031177', '01500701.20040127100031193', '01500701.20040127100031190'], 'size': 7}]
2015-12-10 15:43:59,004 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker2], data=[{'urls': ['01500701.20040127100031053', '01500701.20040127100031050', '01500701.20040127100031168', '01500701.20040127100031055', '01500701.20040127100031173', '01500701.20040128100031262', '01500701.20040127100031175'], 'size': 7}]
2015-12-10 15:44:05,372 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker1], data=[{'urls': ['01500701.20040127100031171', '01500701.20040127100031200', '01500701.20040127100031070', '01500701.20040127100031078', '01500701.20040127100031079', '01500701.20040127100031080', '01500701.20040127100031218'], 'size': 7}]
2015-12-10 15:44:05,825 views.py [19993]: DEBUG NewsUrlList Get Response id=[worker3], data=[{'urls': ['01500701.20040127100031093', '01500701.20040127100031091', '01500701.20040127100031090', '01500701.20040127100031089', '01500701.20040128100031383', '01500701.20040127100031092', '01500701.20040127100031068'], 'size': 7}]

Answer 1

你的问题有点难以理解，但我认为你的意思是 transaction.atomic() 似乎并没有阻止从数据库返回重复行。

简单的回答是，SQL 数据库支持不同的事务隔离级别，而最常见的隔离级别确实不会保护您编写的代码。我对 MySQL/InnoDB 的了解还不够，无法确定，但我怀疑无论您使用什么隔离级别，都可以让两个并发进程在更改之前读取相同的 R 行W 已提交。

通常的解决方案是切换到不同的隔离级别(例如SERIALIZABLE)或使用显式行锁定。无论哪种情况，您都必须对数据库及其配置进行更多研究。