我在一个模型中使用mptt来管理标签系统（每个标签都有一个可选的TreeForeignKey到“父”标签）
每当我需要保存标签模型时，以下查询运行异常缓慢（超过45秒）
UPDATE "taxonomy_taxonomy" SET "tree_id" = ("taxonomy_taxonomy"."tree_id" + %s) WHERE "taxonomy_taxonomy"."tree_id" > %s
我会通过自动化标记系统来发送文章内容，该系统可以生成多达20个标签。显然，这是不可取的 :)
我添加了db_index=False，希望能够改变写入时间（读取似乎不是问题），但问题仍然存在。
以下是相关模型：
class Taxonomy(MPTTModel):
parent = TreeForeignKey('self',blank=True,null=True,related_name='children',verbose_name='Parent', db_index=False)
parent_name = models.CharField(max_length=64, blank=True, null=True, editable=False)
name = models.CharField(verbose_name='Title', max_length=100, db_index=True)
slug = models.SlugField(verbose_name='Slug', blank=True)
primary = models.BooleanField(
verbose_name='Is Primary',
default=False,
db_index=True,
)
type = models.CharField(max_length=30, db_index=True)
created_date = models.DateTimeField(auto_now_add=True, null=True)
updated_date = models.DateTimeField(auto_now=True, null=True)
publication_date = models.DateTimeField(null=True, blank=True)
scheduled_date = models.DateTimeField(null=True, blank=True)
workflowstate = models.CharField(max_length=30, default='draft')
created_by = models.ForeignKey(User, null=True)
paid_content = models.BooleanField(verbose_name='Is Behind the Paywall', default=False, blank=True)
publish_now = True
show_preview = False
temporary = models.BooleanField(default=False)
def save(self, *args, **kwargs):
if self.slug is None:
self.slug = self.name
if not self.slug:
self.slug = slugify(self.name)[:50]
if self.parent:
self.parent_name = self.parent.name
self.slug = slugify(self.slug)
self.workflowstate = "published"
super(Taxonomy, self).save(*args, **kwargs)
store_to_backend_mongo(self)
publish_to_frontend(self)
查询计划（由New Relic报告）：
1) Update on taxonomy_taxonomy (cost=0.00..133833.19 rows=90515 width=139)
2) -> Seq Scan on taxonomy_taxonomy (cost=0.00..133833.19 rows=90515 width=139)
3) Filter: ?
最后，是在这样的查询中的回溯信息：
Traceback (most recent call last):
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/newrelic-2.54.0.41/newrelic/api/web_transaction.py", line 711, in __iter__
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/newrelic-2.54.0.41/newrelic/api/web_transaction.py", line 1087, in __call__
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/core/handlers/wsgi.py", line 189, in __call__
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/core/handlers/base.py", line 132, in get_response
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/newrelic-2.54.0.41/newrelic/hooks/framework_django.py", line 499, in wrapper
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/contrib/auth/decorators.py", line 22, in _wrapped_view
File "./editorial/views.py", line 242, in calculate_queryly
File "./editorial/views.py", line 292, in queryly_function
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/db/models/manager.py", line 127, in manager_method
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/db/models/query.py", line 348, in create
File "./taxonomy/models.py", line 179, in save
File "./taxonomy/models.py", line 58, in save
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/mptt/models.py", line 946, in save
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/mptt/models.py", line 702, in insert_at
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/mptt/managers.py", line 467, in insert_node
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/mptt/managers.py", line 491, in insert_node
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/mptt/managers.py", line 726, in _create_tree_space
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/mptt/managers.py", line 364, in _mptt_update
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/db/models/query.py", line 563, in update
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/db/models/sql/compiler.py", line 1062, in execute_sql
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/db/models/sql/compiler.py", line 840, in execute_sql
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/db/backends/utils.py", line 79, in execute
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
File "/data/www/nj-cms/venv/lib/python3.4/site-packages/newrelic-2.54.0.41/newrelic/hooks/database_dbapi2.py", line 22, in execute
有什么办法可以让这些模型保存的速度更快吗？
附加信息： 这是在Postgres中使用psycopg2引擎。 'ENGINE': 'django.db.backends.postgresql_psycopg2'。
第二次编辑： 按照要求，我使用EXPLAIN ANALYZE运行了查询，结果如下：
nj=# EXPLAIN ANALYZE UPDATE "taxonomy_taxonomy" SET "tree_id" = ("taxonomy_taxonomy"."tree_id" + 1) WHERE "taxonomy_taxonomy"."tree_id" > 1;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------
Update on taxonomy_taxonomy (cost=0.00..9588.75 rows=24582 width=132) (actual time=258718.550..258718.550 rows=0 loops=1)
-> Seq Scan on taxonomy_taxonomy (cost=0.00..9588.75 rows=24582 width=132) (actual time=59.956..8271.209 rows=24582 loops=1)
Filter: (tree_id > 1)
Rows Removed by Filter: 2
Planning time: 28.763 ms
Execution time: 258718.661 ms
(6 rows)
db_index=False能够提高性能吗？数据库仍然需要通过 WHERE 子句查找要更新的行。 - Adrián