Postgresql “慢订单”；“字段”；和限制

我有一个简单的查询，必须从表中获得1条记录，记录数约为1400万条：

EXPLAIN ANALYZE SELECT "projects_toolresult"."id", 
"projects_toolresult"."tool_id", 
"projects_toolresult"."status",
"projects_toolresult"."updated_at",
"projects_toolresult"."created_at" FROM 
"projects_toolresult" WHERE 
("projects_toolresult"."status" = 1 AND 
"projects_toolresult"."tool_id" = 21)
 ORDER BY "projects_toolresult"."updated_at"
 DESC LIMIT 1;

奇怪的是，当我在字段中按

updated_命令查询时，我的查询执行60秒

Limit  (cost=0.43..510.94 rows=1 width=151) (actual
time=56754.932..56754.932 rows=0 loops=1)
->  Index Scan using projects_to_updated_266459_idx on projects_toolresult  (cost=0.43..1800549.09 rows=3527 width=151) (actual time=56754.930..56754.930 rows=0 loops=1)
         Filter: ((status = 1) AND (tool_id = 21))
         Rows Removed by Filter: 13709343  Planning time: 0.236 ms  Execution time: 56754.968 ms (6 rows)

无论是
ASC
还是
DESC

但是，如果我按兰德公司（

或无订单订购：

Limit  (cost=23496.10..23496.10 rows=1 width=151) (actual time=447.532..447.532 rows=0 loops=1)
   ->  Sort  (cost=23496.10..23505.20 rows=3642 width=151) (actual time=447.530..447.530 rows=0 loops=1)
         Sort Key: (random())
         Sort Method: quicksort  Memory: 25kB
         ->  Index Scan using projects_toolresult_tool_id_34a3bb16 on projects_toolresult  (cost=0.56..23477.89 rows=3642 width=151) (actual time=447.513..447.513 rows=0 loops=1)
               Index Cond: (tool_id = 21)
               Filter: (status = 1)
               Rows Removed by Filter: 6097
 Planning time: 0.224 ms
 Execution time: 447.571 ms
(10 rows)

它工作得很快

我在和状态字段中更新了

索引（我也尝试了不使用）。我升级了默认postgres设置，使用此生成器增加了值：


这就是这个查询在运行时发生的情况

博士后版本9.5

我的表和索引：

id              | integer                  | not null default nextval('projects_toolresult_id_seq'::regclass)
 status          | smallint                 | not null
 object_id       | integer                  | not null
 created_at      | timestamp with time zone | not null
 content_type_id | integer                  | not null
 tool_id         | integer                  | not null
 updated_at      | timestamp with time zone | not null
 output_data     | text                     | not null
Indexes:
    "projects_toolresult_pkey" PRIMARY KEY, btree (id)
    "projects_toolresult_content_type_id_object_i_71ee2c2e_uniq" UNIQUE CONSTRAINT, btree (content_type_id, object_id, tool_id)
    "projects_to_created_cee389_idx" btree (created_at)
    "projects_to_tool_id_ec7856_idx" btree (tool_id, status)
    "projects_to_updated_266459_idx" btree (updated_at)
    "projects_toolresult_content_type_id_9924d905" btree (content_type_id)
    "projects_toolresult_tool_id_34a3bb16" btree (tool_id)
Check constraints:
    "projects_toolresult_object_id_check" CHECK (object_id >= 0)
    "projects_toolresult_status_check" CHECK (status >= 0)
Foreign-key constraints:
    "projects_toolresult_content_type_id_9924d905_fk_django_co" FOREIGN KEY (content_type_id) REFERENCES django_content_type(id) DEFERRABLE INITIALLY DEFERRED
    "projects_toolresult_tool_id_34a3bb16_fk_projects_tool_id" FOREIGN KEY (tool_id) REFERENCES projects_tool(id) DEFERRABLE INITIALLY DEFERRED

您正在对
状态
和
工具id
上的数据进行过滤，并在
更新的
上进行排序，但这三列都没有单独的索引

添加索引，如下所示：

在项目上创建索引\u工具结果（状态、工具id、更新位置）
不清楚您的问题是什么，您是否有任何现有的Python/Django代码需要优化？这就是Django ORM生成的代码。但我直接在postgres控制台中完成了这个查询。我想我需要删除django标记。看起来您需要在
更新的
列中添加索引。您在
状态
和
工具id
上进行筛选，在
更新的
上进行排序。用这3个字段添加索引。@Nicarus我更新了我的答案并向您显示了索引