Python 为什么Django ORM这么慢？

1。此代码-原始SQL-需要2.6秒：

  *
    all_feeds = Feed.objects.all()

    for feed in all_feeds:
        q_sku = MainData.objects.raw(f'SELECT id as id, COUNT(DISTINCT sku) as "count" FROM imports_maindata WHERE feed_id={feed.id}')
        q_loc = MainData.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT locale) AS "count" FROM imports_maindata WHERE feed_id={feed.id}')
        q_spec = MapSpecs.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT f_feat_id) AS "count" FROM imports_mapspecs WHERE feed_id={feed.id}')
        q_mapped = MapSpecs.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT ic_feat_id) AS "count" FROM imports_mapspecs WHERE feed_id={feed.id} AND ic_feat_id IS NOT NULL')
    
        q_date = MainData.objects.raw(
        f'SELECT id as id, MAX(last_update) as "last_date" FROM imports_maindata WHERE feed_id={feed.id}')
        print(q_sku[0].count, q_loc[0].count, q_spec[0].count, q_mapped[0].count, q_date[0].last_date)*

    *f = Feed.objects.all()
    for feed in f:
        prods_count = f.filter(maindata__feed_id=feed.id).values('maindata__sku').distinct().count()
        
        locales_count = f.filter(maindata__feed_id=feed.id).values_list('maindata__locale', flat=True).distinct()
    
        total_specs = f.filter(mapspecs__feed_id=feed.id).count()
        mapped_specs = f.filter(mapspecs__feed_id=feed.id, mapspecs__ic_feat_id__isnull=False).all().count()
    
        try:
            last_update = f.filter(maindata__feed_id=feed.id).values('maindata__last_update').distinct().order_by('-maindata__last_update').first()['maindata__last_update']
        except TypeError:
            pass*

    *

    f = Feed.objects.all()
    prods = f.annotate(num_prods=Count('maindata__sku', distinct=True))
    locs = f.annotate(num_locs=Count('maindata__locale', distinct=True))
    total_sp_count = f.annotate(num_books=Count('mapspecs__f_feat_id', distinct=True))
    total_sp_mapped = f.filter(mapspecs__ic_feat_id__isnull=False).annotate(
            num_books=Count('mapspecs__ic_feat_id', distinct=True))
    dates = f.annotate(num_books=Max('maindata__last_update'))

*

3。而这一次（仅限ORM）需要3.1秒：

  *
    all_feeds = Feed.objects.all()

    for feed in all_feeds:
        q_sku = MainData.objects.raw(f'SELECT id as id, COUNT(DISTINCT sku) as "count" FROM imports_maindata WHERE feed_id={feed.id}')
        q_loc = MainData.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT locale) AS "count" FROM imports_maindata WHERE feed_id={feed.id}')
        q_spec = MapSpecs.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT f_feat_id) AS "count" FROM imports_mapspecs WHERE feed_id={feed.id}')
        q_mapped = MapSpecs.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT ic_feat_id) AS "count" FROM imports_mapspecs WHERE feed_id={feed.id} AND ic_feat_id IS NOT NULL')
    
        q_date = MainData.objects.raw(
        f'SELECT id as id, MAX(last_update) as "last_date" FROM imports_maindata WHERE feed_id={feed.id}')
        print(q_sku[0].count, q_loc[0].count, q_spec[0].count, q_mapped[0].count, q_date[0].last_date)*

    *f = Feed.objects.all()
    for feed in f:
        prods_count = f.filter(maindata__feed_id=feed.id).values('maindata__sku').distinct().count()
        
        locales_count = f.filter(maindata__feed_id=feed.id).values_list('maindata__locale', flat=True).distinct()
    
        total_specs = f.filter(mapspecs__feed_id=feed.id).count()
        mapped_specs = f.filter(mapspecs__feed_id=feed.id, mapspecs__ic_feat_id__isnull=False).all().count()
    
        try:
            last_update = f.filter(maindata__feed_id=feed.id).values('maindata__last_update').distinct().order_by('-maindata__last_update').first()['maindata__last_update']
        except TypeError:
            pass*

    *

    f = Feed.objects.all()
    prods = f.annotate(num_prods=Count('maindata__sku', distinct=True))
    locs = f.annotate(num_locs=Count('maindata__locale', distinct=True))
    total_sp_count = f.annotate(num_books=Count('mapspecs__f_feat_id', distinct=True))
    total_sp_mapped = f.filter(mapspecs__ic_feat_id__isnull=False).annotate(
            num_books=Count('mapspecs__ic_feat_id', distinct=True))
    dates = f.annotate(num_books=Max('maindata__last_update'))

*

3。使用ORM但方法不同的这个，在3.1-3.2秒内返回：

  *
    all_feeds = Feed.objects.all()

    for feed in all_feeds:
        q_sku = MainData.objects.raw(f'SELECT id as id, COUNT(DISTINCT sku) as "count" FROM imports_maindata WHERE feed_id={feed.id}')
        q_loc = MainData.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT locale) AS "count" FROM imports_maindata WHERE feed_id={feed.id}')
        q_spec = MapSpecs.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT f_feat_id) AS "count" FROM imports_mapspecs WHERE feed_id={feed.id}')
        q_mapped = MapSpecs.objects.raw(
        f'SELECT id as id, COUNT(DISTINCT ic_feat_id) AS "count" FROM imports_mapspecs WHERE feed_id={feed.id} AND ic_feat_id IS NOT NULL')
    
        q_date = MainData.objects.raw(
        f'SELECT id as id, MAX(last_update) as "last_date" FROM imports_maindata WHERE feed_id={feed.id}')
        print(q_sku[0].count, q_loc[0].count, q_spec[0].count, q_mapped[0].count, q_date[0].last_date)*

    *f = Feed.objects.all()
    for feed in f:
        prods_count = f.filter(maindata__feed_id=feed.id).values('maindata__sku').distinct().count()
        
        locales_count = f.filter(maindata__feed_id=feed.id).values_list('maindata__locale', flat=True).distinct()
    
        total_specs = f.filter(mapspecs__feed_id=feed.id).count()
        mapped_specs = f.filter(mapspecs__feed_id=feed.id, mapspecs__ic_feat_id__isnull=False).all().count()
    
        try:
            last_update = f.filter(maindata__feed_id=feed.id).values('maindata__last_update').distinct().order_by('-maindata__last_update').first()['maindata__last_update']
        except TypeError:
            pass*

    *

    f = Feed.objects.all()
    prods = f.annotate(num_prods=Count('maindata__sku', distinct=True))
    locs = f.annotate(num_locs=Count('maindata__locale', distinct=True))
    total_sp_count = f.annotate(num_books=Count('mapspecs__f_feat_id', distinct=True))
    total_sp_mapped = f.filter(mapspecs__ic_feat_id__isnull=False).annotate(
            num_books=Count('mapspecs__ic_feat_id', distinct=True))
    dates = f.annotate(num_books=Max('maindata__last_update'))

*

---

那么为什么Django ORM如此低效和缓慢呢？计时适用于以DB为单位的少量行（低于50K）。。。因此，它不仅比原始SQL慢，而且语法更加混乱（有时过于模糊）。我想应该考虑其他一些Python框架…

您能提供您从哪里开始测量代码中的时间吗？您能提供您从哪里开始测量代码中的时间吗？