Postgres 数据库 pg_dump - 转储文件详细解释

我用 pg_dump 创建了一个 postgres 数据库转储。我现在想知道为什么备份文件如此冗长。

a) 此配置的目的是什么：

SET statement_timeout = 0;
SET lock_timeout = 0;
SET idle_in_transaction_session_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SELECT pg_catalog.set_config('search_path', '', false);
SET check_function_bodies = false;
SET xmloption = content;
SET client_min_messages = warning;
SET row_security = off;
SET default_tablespace = '';
SET default_table_access_method = heap;

b) 为什么创建表如此冗长：

CREATE TABLE public.tag (
    id integer NOT NULL,
    name character varying(100) NOT NULL,
    description text
);

ALTER TABLE public.tag OWNER TO postgres;

CREATE SEQUENCE public.tag_id_seq
    AS integer
    START WITH 1
    INCREMENT BY 1
    NO MINVALUE
    NO MAXVALUE
    CACHE 1;

ALTER TABLE public.tag_id_seq OWNER TO postgres;
ALTER SEQUENCE public.tag_id_seq OWNED BY public.tag.id;
ALTER TABLE ONLY public.tag ALTER COLUMN id SET DEFAULT nextval('public.tag_id_seq'::regclass);

为什么不像我之前创建的那样：

CREATE TABLE tag (
  id SERIAL PRIMARY KEY, 
  name VARCHAR(100) NOT NULL,
  description TEXT
);

c) 为什么COPY ... FROM stdin;使用而不是INSERT INTO ... VALUES？

COPY public.tag (id, name, description) FROM stdin;
1   vegetarian  No animals.
2   vegan   No animal products.
3   vegetable   
\.

SELECT pg_catalog.setval('public.tag_id_seq', 3, true);

ALTER TABLE ONLY public.tag
    ADD CONSTRAINT tag_pkey PRIMARY KEY (id);