我有一个奇怪的问题，数据库由主表中的大约 27,000 个项目组成，并且以多对多链接这些项目的方式大约有 400,000 个项目。该数据库是一个 Postgresql，从 Psycopg2 运行，在 Apache2 上的 Mod_wsgi 上的 Django 服务器上。
此特定视图的渲染速度会减慢到 10-20 秒。
我很难找到这种放缓的来源。简单的日志记录告诉我，视图实际渲染的时间不到 75 毫秒，因此不是视图逻辑或模板。为视图执行的 SQL 查询总共需要大约 35 毫秒。所以有几秒钟的操作我看不到发生。
分析告诉我：
ncalls tottime percall cumtime percall filename:lineno(function)
5597 3.750 0.001 3.820 0.001 /usr/local/lib/python2.7/dist-packages/django/db/backends/postgresql_psycopg2/base.py:52(execute)
303114/66508 2.518 0.000 5.290 0.000 /usr/lib/python2.7/copy.py:145(deepcopy)
297634 0.762 0.000 0.762 0.000 /usr/lib/python2.7/copy.py:267(_keep_alive)
16627 0.622 0.000 6.145 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:242(clone)
44159/22079 0.449 0.000 2.531 0.000 /usr/lib/python2.7/copy.py:234(_deepcopy_tuple)
5597 0.423 0.000 4.653 0.001 /usr/local/lib/python2.7/dist-packages/django/db/backends/util.py:37(execute)
38706/33254 0.374 0.000 2.970 0.000 /usr/local/lib/python2.7/dist-packages/django/utils/tree.py:55(__deepcopy__)
10961 0.367 0.000 0.599 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/base.py:326(__init__)
16558 0.322 0.000 8.946 0.001 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:241(iterator)
5597 0.293 0.000 2.071 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py:56(as_sql)
5602 0.266 0.000 0.983 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:1035(add_filter)
5597 0.232 0.000 0.540 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py:242(get_default_columns)
94039/83135 0.221 0.000 1.783 0.000 /usr/lib/python2.7/copy.py:226(_deepcopy_list)
44448 0.216 0.000 0.216 0.000 /usr/local/lib/python2.7/dist-packages/django/utils/datastructures.py:121(__init__)
22209 0.207 0.000 0.207 0.000 /usr/lib/python2.7/encodings/utf_8.py:15(decode)
22080 0.199 0.000 1.550 0.000 /usr/lib/python2.7/copy.py:306(_reconstruct)
5723 0.198 0.000 15.201 0.003 /usr/local/lib/python2.7/dist-packages/django/db/models/fields/related.py:367(__get__)
5597 0.194 0.000 0.323 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:104(__init__)
16627 0.179 0.000 6.396 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:904(_clone)
66702 0.174 0.000 0.174 0.000 /usr/local/lib/python2.7/dist-packages/django/utils/tree.py:18(__init__)
5597 0.162 0.000 0.787 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py:162(get_columns)
5597 0.161 0.000 0.302 0.000 /usr/local/lib/python2.7/dist-packages/django/db/backends/postgresql_psycopg2/base.py:160(_cursor)
44448 0.159 0.000 0.159 0.000 /usr/local/lib/python2.7/dist-packages/django/utils/datastructures.py:116(__new__)
11182 0.149 0.000 0.304 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py:854()
16627 0.145 0.000 0.315 0.000 /usr/local/lib/python2.7/dist-packages/django/utils/datastructures.py:136(__deepcopy__)
40271 0.140 0.000 0.209 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py:40(quote_name_unless_alias)
16558 0.131 0.000 7.713 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py:763(results_iter)
34669 0.129 0.000 0.129 0.000 /usr/local/lib/python2.7/dist-packages/django/db/backends/postgresql_psycopg2/operations.py:71(quote_name)
16796/11194 0.128 0.000 0.689 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/where.py:76(as_sql)
22224 0.123 0.000 0.446 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:36(__init__)
1 0.115 0.115 0.115 0.115 /usr/local/lib/python2.7/dist-packages/psycopg2/__init__.py:119(connect)
5437 0.112 0.000 14.141 0.003 /usr/local/lib/python2.7/dist-packages/django/db/models/query.py:374(get)
5598 0.111 0.000 1.232 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:1235(add_q)
1 0.109 0.109 0.109 0.109 /usr/local/lib/python2.7/dist-packages/django/template/loaders/filesystem.py:33(load_template_source)
5602 0.108 0.000 0.561 0.000 /usr/local/lib/python2.7/dist-packages/django/db/models/sql/where.py:148(make_atom)
所以看起来对 Base.py 和 deepcopy 进行了数千次调用，但是当我查看视图的 connection.queries 值时，总共只有 7 个，总共大约 35 毫秒。
有没有人遇到过这个问题？我的视图代码中没有循环，都是正常的启发式、基于 pk 的查找和保存。