sql – 当使用`delete()`时,如何防止django在内存中加载对象？

来自Django文档：

Django needs to fetch objects into memory to send signals and handle cascades. However,if there are no cascades and no signals,then Django may take a fast-path and delete objects without fetching into memory. For large deletes this can result in significantly reduced memory usage. The amount of executed queries can be reduced,too.

https://docs.djangoproject.com/en/1.8/ref/models/querysets/#delete

我不使用信号.我在我试图删除的模型上有外键,但我不明白为什么Django需要将对象加载到内存中.它看起来确实如此,因为我的内存随着查询的运行而上升.

解决方法

import gc

def queryset_iterator(qs,batchsize = 500,gc_collect = True):
    iterator = qs.values_list('pk',flat=True).order_by('pk').distinct().iterator()
    eof = False
    while not eof:
        primary_key_buffer = []
        try:
            while len(primary_key_buffer) < batchsize:
                primary_key_buffer.append(iterator.next())
        except StopIteration:
            eof = True
        for obj in qs.filter(pk__in=primary_key_buffer).order_by('pk').iterator():
            yield obj
        if gc_collect:
            gc.collect()

然后,您可以使用该函数迭代要删除的对象：

for obj in queryset_iterator(HugeQueryset.objects.all()):
    obj.delete()

有关更多信息,请查看this blog post.

（编辑：李大同）

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