使用索引扫描向后改进SQL语句

Question

我们使用的是使用ORM作为数据库请求（PostgreSQL）的Python软件Odoo。目前我正试图减少一些SQL语句的执行时间。我可以通过添加一些索引来增加时间。

现在我有一个查询花费很多时间，不能减少执行时间。你能帮我提高查询的速度吗？我不能改变查询本身（可能只是一些小部分），但也许我们可以改变表结构本身的东西？

查询：

SELECT "purchase_order".id 
FROM "mail_message" AS "purchase_order__message_ids", 
    "mail_notification" AS "purchase_order__message_ids__notification_ids", 
    "purchase_order" 
WHERE ("purchase_order"."id"="purchase_order__message_ids"."res_id" 
     AND "purchase_order__message_ids"."id"="purchase_order__message_ids__notification_ids"."message_id") 
    AND ((("purchase_order"."state" NOT IN ('draft', 
              'sent', 
              'bid', 
              'confirmed')) 
     OR "purchase_order"."state" IS NULL) 
     AND (("purchase_order__message_ids"."model" = 'purchase.order') 
      AND (("purchase_order__message_ids__notification_ids"."partner_id" IN (3)) 
       AND ("purchase_order__message_ids__notification_ids"."is_read" IS NULL 
         OR "purchase_order__message_ids__notification_ids"."is_read" = FALSE)))) 
ORDER BY "purchase_order"."id" DESC LIMIT 100; 

这是EXPLAIN输出分析一下：

# EXPLAIN ANALYZE SELECT "purchase_order".id FROM "mail_message" as "purchase_order__message_ids","mail_notification" as "purchase_order__message_ids__notification_ids","purchase_order" WHERE ("purchase_order"."id"="purchase_order__message_ids"."res_id" AND "purchase_order__message_ids"."id"="purchase_order__message_ids__notification_ids"."message_id") AND ((("purchase_order"."state" not in ('draft','sent','bid','confirmed')) OR "purchase_order"."state" IS NULL) AND (("purchase_order__message_ids"."model" = 'purchase.order') AND (("purchase_order__message_ids__notification_ids"."partner_id" in (3)) AND ("purchase_order__message_ids__notification_ids"."is_read" IS NULL or "purchase_order__message_ids__notification_ids"."is_read" = false)))) ORDER BY "purchase_order"."id" DESC limit 100; 
                             QUERY PLAN                           
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
Limit (cost=0.99..10720.11 rows=100 width=4) (actual time=956.615..958.683 rows=2 loops=1) 
    -> Nested Loop (cost=0.99..63779.73 rows=595 width=4) (actual time=956.609..958.669 rows=2 loops=1) 
     -> Nested Loop (cost=0.71..63177.50 rows=1325 width=4) (actual time=956.573..958.609 rows=2 loops=1) 
       -> Index Scan Backward using mail_message_res_id_index on mail_message purchase_order__message_ids (cost=0.42..48385.44 rows=40025 width=8) (actual time=110.607..518.171 rows=40149 loops=1) 
        Filter: ((model)::text = 'purchase.order'::text) 
        Rows Removed by Filter: 254269 
       -> Index Scan using mail_notification_message_id_index on mail_notification purchase_order__message_ids__notification_ids (cost=0.29..0.36 rows=1 width=4) (actual time=0.006..0.006 rows=0 loops=40149) 
        Index Cond: (message_id = purchase_order__message_ids.id) 
        Filter: (((is_read IS NULL) OR (NOT is_read)) AND (partner_id = 3)) 
        Rows Removed by Filter: 0 
     -> Index Scan using purchase_order_pkey on purchase_order (cost=0.28..0.44 rows=1 width=4) (actual time=0.017..0.019 rows=1 loops=2) 
       Index Cond: (id = purchase_order__message_ids.res_id) 
       Filter: (((state)::text <> ALL ('{draft,sent,bid,confirmed}'::text[])) OR (state IS NULL)) 
Planning time: 2.468 ms 
Execution time: 958.792 ms 
(15 rows) 

您可以观看http://explain.depesz.com/s/cbG

只是笔记的解释 - 行数：

  table   | num_rows 
--------------------------+---------- 
public.mail_notification | 42254 
public.mail_message  | 294474 
public.purchase_order |  6566 
(3 rows) 

这里是\d mail_message输出：

# \d mail_message 
             Table "public.mail_message" 
    Column  |   Type    |       Modifiers       
----------------+-----------------------------+----------------------------------------------------------- 
id    | integer      | not null default nextval('mail_message_id_seq'::regclass) 
create_uid  | integer      | 
create_date | timestamp without time zone | 
write_date  | timestamp without time zone | 
write_uid  | integer      | 
body   | text      | 
model   | character varying(128)  | 
record_name | character varying   | 
date   | timestamp without time zone | 
subject  | character varying   | 
message_id  | character varying   | 
parent_id  | integer      | 
res_id   | integer      | 
subtype_id  | integer      | 
author_id  | integer      | 
type   | character varying   | 
email_from  | character varying   | 
mail_server_id | integer      | 
no_auto_thread | boolean      | 
reply_to  | character varying   | 
Indexes: 
    "mail_message_pkey" PRIMARY KEY, btree (id) 
    "mail_message_author_id_index" btree (author_id) 
    "mail_message_message_id_index" btree (message_id) 
    "mail_message_model_index" btree (model) 
    "mail_message_model_res_id_idx" btree (model, res_id) 
    "mail_message_parent_id_index" btree (parent_id) 
    "mail_message_res_id_index" btree (res_id) 
    "mail_message_subtype_id_index" btree (subtype_id) 
Foreign-key constraints: 
    "mail_message_author_id_fkey" FOREIGN KEY (author_id) REFERENCES res_partner(id) ON DELETE SET NULL 
    "mail_message_create_uid_fkey" FOREIGN KEY (create_uid) REFERENCES res_users(id) ON DELETE SET NULL 
    "mail_message_mail_server_id_fkey" FOREIGN KEY (mail_server_id) REFERENCES ir_mail_server(id) ON DELETE SET NULL 
    "mail_message_parent_id_fkey" FOREIGN KEY (parent_id) REFERENCES mail_message(id) ON DELETE SET NULL 
    "mail_message_subtype_id_fkey" FOREIGN KEY (subtype_id) REFERENCES mail_message_subtype(id) ON DELETE SET NULL 
    "mail_message_write_uid_fkey" FOREIGN KEY (write_uid) REFERENCES res_users(id) ON DELETE SET NULL 
Referenced by: 
    TABLE "crm_lead_forward_to_partner" CONSTRAINT "crm_lead_forward_to_partner_parent_id_fkey" FOREIGN KEY (parent_id) REFERENCES mail_message(id) ON DELETE SET NULL 
    TABLE "mail_compose_message" CONSTRAINT "mail_compose_message_parent_id_fkey" FOREIGN KEY (parent_id) REFERENCES mail_message(id) ON DELETE SET NULL 
    TABLE "mail_mail" CONSTRAINT "mail_mail_mail_message_id_fkey" FOREIGN KEY (mail_message_id) REFERENCES mail_message(id) ON DELETE CASCADE 
    TABLE "mail_message" CONSTRAINT "mail_message_parent_id_fkey" FOREIGN KEY (parent_id) REFERENCES mail_message(id) ON DELETE SET NULL 
    TABLE "mail_message_res_partner_rel" CONSTRAINT "mail_message_res_partner_rel_mail_message_id_fkey" FOREIGN KEY (mail_message_id) REFERENCES mail_message(id) ON DELETE CASCADE 
    TABLE "mail_notification_bcc" CONSTRAINT "mail_notification_bcc_message_id_fkey" FOREIGN KEY (message_id) REFERENCES mail_message(id) ON DELETE CASCADE 
    TABLE "mail_notification_cc" CONSTRAINT "mail_notification_cc_message_id_fkey" FOREIGN KEY (message_id) REFERENCES mail_message(id) ON DELETE CASCADE 
    TABLE "mail_notification" CONSTRAINT "mail_notification_message_id_fkey" FOREIGN KEY (message_id) REFERENCES mail_message(id) ON DELETE CASCADE 
    TABLE "mail_vote" CONSTRAINT "mail_vote_message_id_fkey" FOREIGN KEY (message_id) REFERENCES mail_message(id) ON DELETE CASCADE 
    TABLE "message_attachment_rel" CONSTRAINT "message_attachment_rel_message_id_fkey" FOREIGN KEY (message_id) REFERENCES mail_message(id) ON DELETE CASCADE 

Answer 1

您可以为特定的查询选择指数，像

CREATE INDEX idx_order_messages on mail_message (id) where model = 'purchase.order' 

较少较小的指数结果读取等特点，因此它必须是更快。