问题 PostgreSQL - “多态表”与3个表

我正在使用PostgreSQL 9.5（但升级可以说是9.6）。

我有权限表：

CREATE TABLE public.permissions
(
  id integer NOT NULL DEFAULT nextval('permissions_id_seq'::regclass),
  item_id integer NOT NULL,
  item_type character varying NOT NULL,
  created_at timestamp without time zone NOT NULL,
  updated_at timestamp without time zone NOT NULL,
  CONSTRAINT permissions_pkey PRIMARY KEY (id)
)
-- skipping indices declaration, but they would be present
-- on item_id, item_type

3个表用于多对多关联

-companies_permissions（+指数声明）

CREATE TABLE public.companies_permissions
(
  id integer NOT NULL DEFAULT nextval('companies_permissions_id_seq'::regclass),
  company_id integer,
  permission_id integer,
  CONSTRAINT companies_permissions_pkey PRIMARY KEY (id),
  CONSTRAINT fk_rails_462a923fa2 FOREIGN KEY (company_id)
      REFERENCES public.companies (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fk_rails_9dd0d015b9 FOREIGN KEY (permission_id)
      REFERENCES public.permissions (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)

CREATE INDEX index_companies_permissions_on_company_id
  ON public.companies_permissions
  USING btree
  (company_id);

CREATE INDEX index_companies_permissions_on_permission_id
  ON public.companies_permissions
  USING btree
  (permission_id);

CREATE UNIQUE INDEX index_companies_permissions_on_permission_id_and_company_id
  ON public.companies_permissions
  USING btree
  (permission_id, company_id);

-permissions_user_groups（+索引声明）

CREATE TABLE public.permissions_user_groups
(
  id integer NOT NULL DEFAULT nextval('permissions_user_groups_id_seq'::regclass),
  permission_id integer,
  user_group_id integer,
  CONSTRAINT permissions_user_groups_pkey PRIMARY KEY (id),
  CONSTRAINT fk_rails_c1743245ea FOREIGN KEY (permission_id)
      REFERENCES public.permissions (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fk_rails_e966751863 FOREIGN KEY (user_group_id)
      REFERENCES public.user_groups (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)

CREATE UNIQUE INDEX index_permissions_user_groups_on_permission_and_user_group
  ON public.permissions_user_groups
  USING btree
  (permission_id, user_group_id);

CREATE INDEX index_permissions_user_groups_on_permission_id
  ON public.permissions_user_groups
  USING btree
  (permission_id);

CREATE INDEX index_permissions_user_groups_on_user_group_id
  ON public.permissions_user_groups
  USING btree
  (user_group_id);

-permissions_users（+索引声明）

CREATE TABLE public.permissions_users
(
  id integer NOT NULL DEFAULT nextval('permissions_users_id_seq'::regclass),
  permission_id integer,
  user_id integer,
  CONSTRAINT permissions_users_pkey PRIMARY KEY (id),
  CONSTRAINT fk_rails_26289d56f4 FOREIGN KEY (user_id)
      REFERENCES public.users (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fk_rails_7ac7e9f5ad FOREIGN KEY (permission_id)
      REFERENCES public.permissions (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)

CREATE INDEX index_permissions_users_on_permission_id
  ON public.permissions_users
  USING btree
  (permission_id);

CREATE UNIQUE INDEX index_permissions_users_on_permission_id_and_user_id
  ON public.permissions_users
  USING btree
  (permission_id, user_id);

CREATE INDEX index_permissions_users_on_user_id
  ON public.permissions_users
  USING btree
  (user_id);

我将不得不像这样运行SQL查询很多次：

SELECT
"permissions".*,
"permissions_users".*,
"companies_permissions".*,
"permissions_user_groups".* 
FROM "permissions"
LEFT OUTER JOIN
  "permissions_users" ON "permissions_users"."permission_id" = "permissions"."id"
LEFT OUTER JOIN
  "companies_permissions" ON "companies_permissions"."permission_id" = "permissions"."id"
LEFT OUTER JOIN
  "permissions_user_groups" ON "permissions_user_groups"."permission_id" = "permissions"."id"
WHERE
  (companies_permissions.company_id = <company_id> OR
  permissions_users.user_id in (<user_ids> OR NULL) OR
  permissions_user_groups.user_group_id IN (<user_group_ids> OR NULL)) AND
permissions.item_type = 'Topic' 

假设我们在其他表中拥有大约10000多个权限和类似数量的记录。

我需要担心性能吗？

我的意思是......我有4个 LEFT OUTER JOINs它应该很快返回结果（比如说<200ms）。

我正在考虑声明1个“多态”表，例如：

CREATE TABLE public.permissables
(
  id integer NOT NULL DEFAULT nextval('permissables_id_seq'::regclass),
  permission_id integer,
  resource_id integer NOT NULL,
  resource_type character varying NOT NULL,
  created_at timestamp without time zone NOT NULL,
  updated_at timestamp without time zone NOT NULL,
  CONSTRAINT permissables_pkey PRIMARY KEY (id)
)
-- skipping indices declaration, but they would be present

然后我可以像这样运行查询：

SELECT
  permissions.*,
  permissables.*
FROM permissions
LEFT OUTER JOIN
  permissables ON permissables.permission_id = permissions.id
WHERE
  permissions.item_type = 'Topic' AND
  (permissables.owner_id IN (<user_ids>) AND permissables.owner_type = 'User') OR
  (permissables.owner_id = <company_id> AND permissables.owner_type = 'Company') OR
  (permissables.owner_id IN (<user_groups_ids>) AND permissables.owner_type = 'UserGroup')

问题：

1. 哪个选项更好/更快？也许有更好的方法来做到这一点？

a）4桌（permissions, companies_permissions, user_groups_permissions, users_permissions） b）2张桌子（permissions, permissables）

2. 我需要声明不同的索引吗？ btree 上 permissions.item_type ？

3. 我是否需要每天跑几次 vacuum analyze 表使索引工作（两个选项）？

EDIT1：

SQLFiddle示例：

1. wildplasser建议（来自评论），不工作： http://sqlfiddle.com/#!15/9723f8/1
2. 原始查询（4表）： http://sqlfiddle.com/#!15/9723f8/2

{我也在错误的地方删除了反引号，感谢@wildplasser}