Postgresql服务器信息

实例：EC2 m1.xlarge
Postgresql版本：9.1
文章记录：240,695
总内存：14980 MB
shared_buffers：3617MB
effective_cache_size：8000MB
work_mem：40MB
checkpoint_segments：10
maintenance_work_mem：64MB

相关模型

class AuthorsModelMixin(models.Model):

    authors = models.ManyToManyField('people.Person', blank=True)
    nonstaff_authors = models.CharField(
        verbose_name='Non-staff authors', max_length=255, blank=True,
        help_text="Used for the name of the author for non-staff members.")
    byline_title = models.CharField(
        max_length=255, blank=True,
        help_text="Often contains an organization. Title of the person, or " \
                  "entity associated with the byline and a specified person " \
                  "(i.e. Associated Press).")

    class Meta:
        abstract = True

class TaxonomyModelMixin(models.Model):

    sections = models.ManyToManyField(Section, blank=True)
    tags = TaggableManager(
        blank=True, help_text='A comma-separated list of tags (i.e. ' \
                              'Outdoors, Election, My Great News Topic).')

    class Meta:
        abstract = True

class PublishModelMixin(models.Model):

    status_choices = (
        ('D', 'Draft'),
        ('P', 'Published'),
        ('T', 'Trash'),
    )

    comment_choices = (
        ('enabled', 'Enabled'),
        ('disabled', 'Disabled'),
    )

    sites = models.ManyToManyField(Site, default=[1])
    status = models.CharField(
        max_length=1, default='P', db_index=True, choices=status_choices,
        help_text='Only published items will appear on the site')
    published = models.DateTimeField(
        default=timezone.now, db_index=True,
        help_text='Select the date you want the content to be published.')
    is_premium = models.BooleanField(
        choices=((True, 'Yes'), (False, 'No')),
        verbose_name='Premium Content', default=True)
    comments = models.CharField(
        max_length=30, default='enabled',
        choices=comment_choices, help_text='Enable or disable comments.')
    created = models.DateTimeField(auto_now_add=True)
    modified = models.DateTimeField(auto_now=True)
    objects = PublishedManager()

    class Meta:
        abstract = True

class Article(AuthorsModelMixin, TaxonomyModelMixin, PublishModelMixin):

    title = models.CharField(max_length=255)
    slug = SlugModelField(max_length=255)
    lead_photo = models.ForeignKey('media.Photo', blank=True, null=True)
    summary = models.TextField(blank=True)
    body = models.TextField()

我尝试过的查询集

Queryset 1

查询时间：（76毫秒）
优点：快速，没有机会发表文章不会显示
缺点：如果较高的ID具有较旧的发布日期，则文章列表将无序

queryset = Article.objects \
                  .published() \
                  .filter(sections__full_slug__startswith=section.full_slug) \
                  .prefetch_related('lead_photo', 'authors') \
                  .order_by('-id') \
                  .distinct('id')

Queryset 2

查询时间：（76毫秒）
优点：文章始终有序缺点：如果两篇文章具有相同的发布日期和时间，则只列出一个

queryset = Article.objects \
                  .published() \
                  .filter(sections__full_slug__startswith=section.full_slug) \
                  .prefetch_related('lead_photo', 'authors') \
                  .order_by('-published') \
                  .distinct('published')

Queryset 3

查询时间：（1007毫秒）
优点：文章一直在按顺序排列，没有文章没有被列入的机会缺点：慢得多！

queryset = Article.objects \
                  .published() \
                  .filter(sections__full_slug__startswith=section.full_slug) \
                  .prefetch_related('lead_photo', 'authors') \
                  .order_by('-id', '-published') \
                  .distinct('id')

Queryset 4

查询时间：（4797.85 ms）
优点：不多，但不使用DISTINCT ON意味着它适用于SQLite等其他数据库进行测试缺点：慢得多!!!

queryset = Article.objects \
                  .published() \
                  .filter(sections__full_slug__startswith=section.full_slug) \
                  .prefetch_related('lead_photo', 'authors') \
                  .order_by('-published') \
                  .distinct()

Answer 1

您可以尝试对此查询进行性能测试吗？由于您尚未发布模型，请调整任何字段名称。

我的想法是把它分成两个：一个将返回查看中间表的所有文章ID。

queryset = Article.objects \
    .published() \
    .filter(id__in=Article.sections.through.objects
            .filter(section__full_slug__startswith=section.full_slug)
            .values_list('article_id', flat=True)) \
    .prefetch_related('lead_photo', 'authors') \
    .order_by('-published', '-id')

如何加速使用.distinct（）的查询集？