Postgres invalid command \N数据恢复处理

同事做一个单表恢复工作，数据在1000多W，说是报了错误导不进去，环境与流程见下：

OS:CnetOS 5
DB:Postgres 9.2.4

恢复步骤：

1.导出语句
pg_dump -h xxxxx -p 5432 -U postgres -b -Fp  db_test -t t_kenyon -f /var/t_kenyon.bak

2.导入语句
psql -h xxxx -d new_db -U postgres < /var/t_kenyon.bak

3.报错信息，屏幕上一堆的诸如
invalid command \N
invalid command \N
invalid command \N
invalid command \N
invalid command \N
invalid command \N
........

分析处理：

因为是逻辑导出没有压缩定制的文件，故可以查看备份内容
[postgres@localhost ~]$ more t_kenyon.bak 
--
-- PostgreSQL database dump
--

SET statement_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SET check_function_bodies = false;
SET client_min_messages = warning;

SET search_path = public, pg_catalog;

SET default_tablespace = '';

SET default_with_oids = false;

--
-- Name: t_kenyon; Type: TABLE; Schema: public; Owner: postgres; Tablespace: 
--

CREATE TABLE t_kenyon (
    col1 integer DEFAULT nextval('t_kenyon_col1_seq'::regclass) NOT NULL,
    col2 ..
    col3 ..
);


ALTER TABLE public.t_kenyon OWNER TO postgres;

--
-- Name: COLUMN t_kenyon.col; Type: COMMENT; Schema: public; Owner: postgres
--

--
-- Data for Name: t_kenyon; Type: TABLE DATA; Schema: public; Owner: postgres
--

COPY t_kenyon (col1,col2,col3....) FROM stdin;
3315866 \N      1       5.00    \N      \N      \N      2011-01-12 08:37:07+08  1       4130000 爱我中话        \N      708     Kenyon    HZ      雅安加油    HZ01    HELLO    \N      9       \N
3315934 \N      1       5.00    \N      \N      \N      2011-01-12 09:13:17+08  1       4130000 我哎中华        \N      708     kenyon    HZ      雅安加油    
..........此处略去1W字

看起来报错的信息都是\N即空格的地方出错了，检查了一下postgres的日志，有几条信息发现很有意思

2013-04-23 00:16:23.149 PDT,"postgres","postgres",24738,"[local]",51763545.60a2,4,"CREATE TABLE",2013-04-23 00:16:21 PDT,2/331,1856,ERROR,42P01,"relation ""t_kenyon_col1_seq"" does not exist",,,,,,"CREATE TABLE t_kenyon (col1,col2...)..

这看起来是导数据之前的建表失败了，因为sequence不存在，后面的copy操作直接就报了N多的错误，尝试先建一下索引，再重新导入

postgres=#CREATE SEQUENCE t_kenyon_col1_seq  INCREMENT 1  MINVALUE 1  MAXVALUE 9223372036854775807  START 17354062  CACHE 1;
CREATE SEQUENCE
postgres=# \q
[postgres@localhost ~]$ psql -d postgres -U postgres < /var/t_kenyon.bak 
SET
SET
SET
SET
SET
SET
SET
SET
CREATE TABLE
ALTER TABLE
COMMENT
ALTER TABLE
CREATE INDEX
CREATE INDEX
[postgres@localhost ~]$

OK,导入成功。但是有一个问题，为什么pg_dump导出的时候没有把sequence带出来呢？验证一下

[postgres@localhost ~]$ psql
psql (9.2.4)
Type "help" for help.

postgres=# \d
No relations found.
postgres=# create table d_kenyon(id serial,vname varchar(30));
NOTICE:  CREATE TABLE will create implicit sequence "d_kenyon_id_seq" for serial column "d_kenyon.id"
CREATE TABLE
postgres=# insert into d_kenyon(vname) select generate_series(1,10)||'Hi,Kenyon!'; 
INSERT 0 10
postgres=# select * from d_kenyon;
 id |    vname     
----+--------------
  1 | 1Hi,Kenyon!
  2 | 2Hi,Kenyon!
  3 | 3Hi,Kenyon!
  4 | 4Hi,Kenyon!
  5 | 5Hi,Kenyon!
  6 | 6Hi,Kenyon!
  7 | 7Hi,Kenyon!
  8 | 8Hi,Kenyon!
  9 | 9Hi,Kenyon!
 10 | 10Hi,Kenyon!
(10 rows)

postgres=# \d
               List of relations
 Schema |      Name       |   Type   |  Owner   
--------+-----------------+----------+----------
 public | d_kenyon        | table    | postgres
 public | d_kenyon_id_seq | sequence | postgres

[postgres@localhost ~]$ pg_dump -U postgres -b -Fp  postgres -t d_kenyon -f d_kenyon.bak
[postgres@localhost ~]$ more d_kenyon.bak 
--
-- PostgreSQL database dump
--

SET statement_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SET check_function_bodies = false;
SET client_min_messages = warning;

SET search_path = public, pg_catalog;

SET default_tablespace = '';

SET default_with_oids = false;

--
-- Name: d_kenyon; Type: TABLE; Schema: public; Owner: postgres; Tablespace: 
--

CREATE TABLE d_kenyon (
    id integer NOT NULL,
    vname character varying(30)
);


ALTER TABLE public.d_kenyon OWNER TO postgres;

--
-- Name: d_kenyon_id_seq; Type: SEQUENCE; Schema: public; Owner: postgres
--

CREATE SEQUENCE d_kenyon_id_seq
    START WITH 1
    INCREMENT BY 1
    NO MINVALUE
    NO MAXVALUE
    CACHE 1;


ALTER TABLE public.d_kenyon_id_seq OWNER TO postgres;

--
-- Name: d_kenyon_id_seq; Type: SEQUENCE OWNED BY; Schema: public; Owner: postgres
--

ALTER SEQUENCE d_kenyon_id_seq OWNED BY d_kenyon.id;


--
-- Name: id; Type: DEFAULT; Schema: public; Owner: postgres
--

ALTER TABLE ONLY d_kenyon ALTER COLUMN id SET DEFAULT nextval('d_kenyon_id_seq'::regclass);


--
-- Data for Name: d_kenyon; Type: TABLE DATA; Schema: public; Owner: postgres
--

COPY d_kenyon (id, vname) FROM stdin;
1       1Hi,Kenyon!
2       2Hi,Kenyon!
3       3Hi,Kenyon!
4       4Hi,Kenyon!
5       5Hi,Kenyon!
6       6Hi,Kenyon!
7       7Hi,Kenyon!
8       8Hi,Kenyon!
[postgres@localhost ~]$ psql
psql (9.2.4)
Type "help" for help.

postgres=# \d
               List of relations
 Schema |      Name       |   Type   |  Owner   
--------+-----------------+----------+----------
 public | d_kenyon        | table    | postgres
 public | d_kenyon_id_seq | sequence | postgres
(2 rows)

postgres=# drop table d_kenyon;
DROP TABLE
postgres=# \q
[postgres@localhost ~]$ psql < d_kenyon.bak 
SET
SET
SET
SET
SET
SET
SET
SET
CREATE TABLE
ALTER TABLE
CREATE SEQUENCE
ALTER TABLE
ALTER SEQUENCE
ALTER TABLE
 setval 
--------
     10
(1 row)

[postgres@localhost ~]$ 

发现用serial产生的sequence是可以导出并导入的，回过头再去看异常的表，发现该表字段不是serial，模拟一下非serial字段的pg_dump导出情况

postgres=# create table d_test as select * from d_kenyon;
SELECT 10

postgres=# alter table d_test alter column id set default nextval('d_kenyon_id_seq'::regclass);
ALTER TABLE
postgres=# \d d_test
                             Table "public.d_test"
 Column |         Type          |                  Modifiers                   
--------+-----------------------+----------------------------------------------
 id     | integer               | default nextval('d_kenyon_id_seq'::regclass)
 vname  | character varying(30) | 

postgres=# \q
[postgres@localhost ~]$ pg_dump -U postgres -b -Fp  postgres -t d_test -f d_kenyon.bak
[postgres@localhost ~]$ more d_kenyon.bak 
--
-- PostgreSQL database dump
--
SET statement_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SET check_function_bodies = false;
SET client_min_messages = warning;
SET search_path = public, pg_catalog;
SET default_tablespace = '';
SET default_with_oids = false;

--
-- Name: d_test; Type: TABLE; Schema: public; Owner: postgres; Tablespace: 
--

CREATE TABLE d_test (
    id integer DEFAULT nextval('d_kenyon_id_seq'::regclass),
    vname character varying(30)
);

ALTER TABLE public.d_test OWNER TO postgres;

--
-- Data for Name: d_test; Type: TABLE DATA; Schema: public; Owner: postgres
--

COPY d_test (id, vname) FROM stdin;
1       1Hi,Kenyon!
2       2Hi,Kenyon!
3       3Hi,Kenyon!
4       4Hi,Kenyon!
5       5Hi,Kenyon!
6       6Hi,Kenyon!
7       7Hi,Kenyon!
8       8Hi,Kenyon!
9       9Hi,Kenyon!
10      10Hi,Kenyon!
\.

--
-- PostgreSQL database dump complete
--

确实是没有sequence导出来的，查了一下，pg_depend里序列与表并没有关联上，也就是说这样的表与sequence是独立的，可以用以下SQL验证一下表与sequence的关联关系

WITH fq_objects AS (SELECT c.oid,c.relname AS fqname ,c.relkind, c.relname AS relation FROM 
 pg_class c JOIN pg_namespace n ON n.oid = c.relnamespace ),
  sequences AS (SELECT oid,fqname FROM fq_objects WHERE relkind = 'S'), 
     tables    AS (SELECT oid, fqname FROM fq_objects WHERE relkind = 'r' ) 
      SELECT s.fqname AS sequence,'->' as depends,t.fqname AS table
       FROM pg_depend d JOIN sequences s ON s.oid = d.objid 
                 JOIN tables t ON t.oid = d.refobjid 
          WHERE d.deptype = 'a' and t.fqname = 'd_kenyon';

总结： 
扩展开来想，这种备份如果是整个库备份再恢复，应是OK的，后来验证确实如此，故对于整库恢复是不用考虑这个问题的，单表恢复则需要注意一下。