一、介绍
大对象源于large object的翻译，简称lo，与普通的整型、时间类型等不同，它实际存储一些文件、图片等较大尺寸的对象。
内置的lo系统函数
db_big=# \df lo_*
List of functions
Schema | Name | Result data type | Argument data types | Type
------------+---------------+------------------+---------------------------+--------
pg_catalog | lo_close | integer | integer | normal
pg_catalog | lo_creat | oid | integer | normal
pg_catalog | lo_create | oid | oid | normal
pg_catalog | lo_export | integer | oid,text | normal
pg_catalog | lo_import | oid | text | normal
pg_catalog | lo_import | oid | text,oid | normal
pg_catalog | lo_lseek | integer | integer,integer,integer | normal
pg_catalog | lo_lseek64 | bigint | integer,bigint,integer | normal
pg_catalog | lo_open | integer | oid,integer | normal
pg_catalog | lo_tell | integer | integer | normal
pg_catalog | lo_tell64 | bigint | integer | normal
pg_catalog | lo_truncate | integer | integer,integer | normal
pg_catalog | lo_truncate64 | integer | integer,bigint | normal
pg_catalog | lo_unlink | integer | oid | normal
(14 rows)
二、使用
1.创建大对象，导入数据
db_big=# select lo_create(1);
lo_create
-----------
1
(1 row)
--创建一个OID是1但没数据的大对象,该值被插入pg_largeobject_Metadata,OID可以随便指定，但不能与大对象元数据表的OID有重复
db_big=# select oid,* from pg_largeobject_Metadata;
oid | lomowner | lomacl
-----+----------+--------
1 | 10 |
(1 row)
--存储实际对象数据的表是空的
db_big=# select count(1) from pg_largeobject;
count
-------
0
(1 row)
db_big=# create table tab_big(vname text,souroid oid);
CREATE TABLE
db_big=# insert into tab_big values('passwd list',lo_import('/etc/passwd'));
INSERT 0 1
db_big=# select * from tab_big ;
vname | souroid
-------------+---------
passwd list | 20063
(1 row)
db_big=# select oid,* from pg_largeobject_Metadata ;
oid | lomowner | lomacl
-------+----------+--------
1 | 10 |
20063 | 10 |
(2 rows)
--实际存储的数据
db_big=# select * from pg_largeobject;
loid | pageno | data
-------------------------------------------------------------------------------------------------
20063 | 0 | \x726f6f743a783a303a303a726f6f743a2f726f6f743a2f62696e2f626173680a62696e3a783a313a313a62696e3a2f62696e3a2f7362696e2f6e6f6c6f67696e0a6461656d6f6e3a783a323a323a6461656d6f6e3a2f7362696e3a2f7362696e2f6e6f6c6f67696e0a61646d3
a783a333a343a61646d3a2f7661722f61646d3a2f7362696e2f6e6f6c6f67696e0a6c703a783a343a373a6c703a2f7661722f73706f6f6c2f6c70643a2f7362696e2f6e6f6c6f67696e0a73796e633a783a353a303a73796e633a2f7362696e3a2f62696e2f73796e630a73687574646f776e3a783a36
3a303a73687574646f776e3a2f7362696e3a2f7362696e2f73687574646f776e0a68616c743a783a373a303a68616c743a2f7362696e3a2f7362696e2f68616c740a6d61696c3a783a383a31323a6d61696c3a2f7661722f73706f6f6c2f6d61696c3a2f7362696e2f6e6f6c6f67696e0a757563703a7
83a31303a31343a757563703a2f7661722f73706f6f6c2f757563703a2f7362696e2f6e6f6c6f67696e0a6f70657261746f723a783a31313a303a6f70657261746f723a2f726f6f743a2f7362696e2f6e6f6c6f67696e0a67616d65733a783a31323a3130303a67616d65733a2f7573722f67616d6573
3a2f7362696e2f6e6f6c6f67696e0a676f706865723a783a31333a33303a676f706865723a2f7661722f676f706865723a2f7362696e2f6e6f6c6f67696e0a6674703a783a31343a35303a46545020557365723a2f7661722f6674703a2f7362696e2f6e6f6c6f67696e0a6e6f626f64793a783a39393
a39393a4e6f626f64793a2f3a2f7362696e2f6e6f6c6f67696e0a646275733a783a38313a38313a53797374656d206d657373616765206275733a2f3a2f7362696e2f6e6f6c6f67696e0a766373613a783a36393a36393a7669727475616c20636f6e736f6c65206d656d6f7279206f776e65723a2f64
65763a2f7362696e2f6e6f6c6f67696e0a7361736c617574683a783a3439393a37363a225361736c61757468642075736572223a2f7661722f656d7074792f7361736c617574683a2f7362696e2f6e6f6c6f67696e0a706f73746669783a783a38393a38393a3a2f7661722f73706f6f6c2f706f73746
669783a2f7362696e2f6e6f6c6f67696e0a61766168693a783a37303a37303a4176616869206d444e532f444e532d534420537461636b3a2f7661722f72756e2f61766168692d6461656d6f6e3a2f7362696e2f6e6f6c6f67696e0a737368643a783a37343a37343a50726976696c6567652d73657061
7261746564205353483a2f7661722f656d7074792f737368643a2f7362696e2f6e6f6c6f67696e0a706f7374677265733a783a3530303a3530303a3a2f686f6d652f706f7374677265733a2f62696e2f626173680a6170616368653a783a34383a34383a4170616368653a2f7661722f7777773a2f736
2696e2f6e6f6c6f67696e0a7a61626269783a783a3530313a3530313a3a2f686f6d652f7a61626269783a2f62696e2f626173680a
--指定oid存储
db_big=# insert into tab_big values('passwd list',lo_import('/etc/passwd',123));
INSERT 0 1
db_big=# select oid,* from pg_largeobject_Metadata ;
oid | lomowner | lomacl
-------+----------+--------
1 | 10 |
20063 | 10 |
123 | 10 |
db_big=# select * from pg_largeobject;
loid | pageno | data
20063 | 0 | \x726f6f743a783a303a303a726f6f743a2f726f6f743a2f62696e2f626173680a62696e3a783a313a313a62696e3a2f62696e3a2f7362696e2f6e6f6c6f67696e0a6461656d6f6e3a783a323a323a6461656d6f6e3a2f7362696e3a2f7362696e2f6e6f6c6f67696e0a61646d3
a783a333a343a61646d3a2f7661722f61646d3a2f7362696e2f6e6f6c6f67696e0a6c703a783a343a373a6c703a2f7661722f73706f6f6c2f6c70643a2f7362696e2f6e6f6c6f67696e0a73796e633a783a353a303a73796e633a2f7362696e3a2f62696e2f73796e630a73687574646f776e3a783a36
3a303a73687574646f776e3a2f7362696e3a2f7362696e2f73687574646f776e0a68616c743a783a373a303a68616c743a2f7362696e3a2f7362696e2f68616c740a6d61696c3a783a383a31323a6d61696c3a2f7661722f73706f6f6c2f6d61696c3a2f7362696e2f6e6f6c6f67696e0a757563703a7
83a31303a31343a757563703a2f7661722f73706f6f6c2f757563703a2f7362696e2f6e6f6c6f67696e0a6f70657261746f723a783a31313a303a6f70657261746f723a2f726f6f743a2f7362696e2f6e6f6c6f67696e0a67616d65733a783a31323a3130303a67616d65733a2f7573722f67616d6573
3a2f7362696e2f6e6f6c6f67696e0a676f706865723a783a31333a33303a676f706865723a2f7661722f676f706865723a2f7362696e2f6e6f6c6f67696e0a6674703a783a31343a35303a46545020557365723a2f7661722f6674703a2f7362696e2f6e6f6c6f67696e0a6e6f626f64793a783a39393
a39393a4e6f626f64793a2f3a2f7362696e2f6e6f6c6f67696e0a646275733a783a38313a38313a53797374656d206d657373616765206275733a2f3a2f7362696e2f6e6f6c6f67696e0a766373613a783a36393a36393a7669727475616c20636f6e736f6c65206d656d6f7279206f776e65723a2f64
65763a2f7362696e2f6e6f6c6f67696e0a7361736c617574683a783a3439393a37363a225361736c61757468642075736572223a2f7661722f656d7074792f7361736c617574683a2f7362696e2f6e6f6c6f67696e0a706f73746669783a783a38393a38393a3a2f7661722f73706f6f6c2f706f73746
669783a2f7362696e2f6e6f6c6f67696e0a61766168693a783a37303a37303a4176616869206d444e532f444e532d534420537461636b3a2f7661722f72756e2f61766168692d6461656d6f6e3a2f7362696e2f6e6f6c6f67696e0a737368643a783a37343a37343a50726976696c6567652d73657061
7261746564205353483a2f7661722f656d7074792f737368643a2f7362696e2f6e6f6c6f67696e0a706f7374677265733a783a3530303a3530303a3a2f686f6d652f706f7374677265733a2f62696e2f626173680a6170616368653a783a34383a34383a4170616368653a2f7661722f7777773a2f736
2696e2f6e6f6c6f67696e0a7a61626269783a783a3530313a3530313a3a2f686f6d652f7a61626269783a2f62696e2f626173680a
123 | 0 | \x726f6f743a783a303a303a726f6f743a2f726f6f743a2f62696e2f626173680a62696e3a783a313a313a62696e3a2f62696e3a2f7362696e2f6e6f6c6f67696e0a6461656d6f6e3a783a323a323a6461656d6f6e3a2f7362696e3a2f7362696e2f6e6f6c6f67696e0a61646d3
a783a333a343a61646d3a2f7661722f61646d3a2f7362696e2f6e6f6c6f67696e0a6c703a783a343a373a6c703a2f7661722f73706f6f6c2f6c70643a2f7362696e2f6e6f6c6f67696e0a73796e633a783a353a303a73796e633a2f7362696e3a2f62696e2f73796e630a73687574646f776e3a783a36
3a303a73687574646f776e3a2f7362696e3a2f7362696e2f73687574646f776e0a68616c743a783a373a303a68616c743a2f7362696e3a2f7362696e2f68616c740a6d61696c3a783a383a31323a6d61696c3a2f7661722f73706f6f6c2f6d61696c3a2f7362696e2f6e6f6c6f67696e0a757563703a7
83a31303a31343a757563703a2f7661722f73706f6f6c2f757563703a2f7362696e2f6e6f6c6f67696e0a6f70657261746f723a783a31313a303a6f70657261746f723a2f726f6f743a2f7362696e2f6e6f6c6f67696e0a67616d65733a783a31323a3130303a67616d65733a2f7573722f67616d6573
3a2f7362696e2f6e6f6c6f67696e0a676f706865723a783a31333a33303a676f706865723a2f7661722f676f706865723a2f7362696e2f6e6f6c6f67696e0a6674703a783a31343a35303a46545020557365723a2f7661722f6674703a2f7362696e2f6e6f6c6f67696e0a6e6f626f64793a783a39393
a39393a4e6f626f64793a2f3a2f7362696e2f6e6f6c6f67696e0a646275733a783a38313a38313a53797374656d206d657373616765206275733a2f3a2f7362696e2f6e6f6c6f67696e0a766373613a783a36393a36393a7669727475616c20636f6e736f6c65206d656d6f7279206f776e65723a2f64
65763a2f7362696e2f6e6f6c6f67696e0a7361736c617574683a783a3439393a37363a225361736c61757468642075736572223a2f7661722f656d7074792f7361736c617574683a2f7362696e2f6e6f6c6f67696e0a706f73746669783a783a38393a38393a3a2f7661722f73706f6f6c2f706f73746
669783a2f7362696e2f6e6f6c6f67696e0a61766168693a783a37303a37303a4176616869206d444e532f444e532d534420537461636b3a2f7661722f72756e2f61766168692d6461656d6f6e3a2f7362696e2f6e6f6c6f67696e0a737368643a783a37343a37343a50726976696c6567652d73657061
7261746564205353483a2f7661722f656d7074792f737368643a2f7362696e2f6e6f6c6f67696e0a706f7374677265733a783a3530303a3530303a3a2f686f6d652f706f7374677265733a2f62696e2f626173680a6170616368653a783a34383a34383a4170616368653a2f7661722f7777773a2f736
2696e2f6e6f6c6f67696e0a7a61626269783a783a3530313a3530313a3a2f686f6d652f7a61626269783a2f62696e2f626173680a
(2 rows)
2.实际的存储
--大对象数据表，pageno是一个大对象在该表里实际存储的条数，每条大小是block_size，默认是8kb
db_big=# show block_size ;
block_size
------------
8192
(1 row)
db_big=# \d+ pg_largeobject
Table "pg_catalog.pg_largeobject"
Column | Type | Modifiers | Storage | Stats target | Description
--------+---------+-----------+----------+--------------+-------------
loid | oid | not null | plain | |
pageno | integer | not null | plain | |
data | bytea | | extended | |
Indexes:
"pg_largeobject_loid_pn_index" UNIQUE,btree (loid,pageno)
Has OIDs: no
--大对象元数据表
db_big=# \d+ pg_largeobject_Metadata，隐藏的oid是唯一约束
Table "pg_catalog.pg_largeobject_Metadata"
Column | Type | Modifiers | Storage | Stats target | Description
----------+-----------+-----------+----------+--------------+-------------
lomowner | oid | not null | plain | |
lomacl | aclitem[] | | extended | |
Indexes:
"pg_largeobject_Metadata_oid_index" UNIQUE,btree (oid)
Has OIDs: yes
(1 row)
3.大对象的导出
db_big=# select lo_export(123,'/home/pwd.list');
ERROR: could not create server file "/home/pwd.list": Permission denied
db_big=# select lo_export(123,'/home/postgres/pwd.list');
lo_export
-----------
1
(1 row)
--返回1表示成功
[postgres@db1 ~]$ more /home/postgres/pwd.list
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
......
4.大对象的删除
--自带有一个lo_unlink函数来清理大对象数据,类似于普通表的delete命令
db_big=# select lo_unlink(123);
lo_unlink
-----------
1
(1 row)
db_big=# select lo_unlink(1);
lo_unlink
-----------
1
(1 row)
db_big=# select oid,* from pg_largeobject_Metadata ;
oid | lomowner | lomacl
-------+----------+--------
20063 | 10 |
(1 row)
db_big=# select * from pg_largeobject;
loid | pageno | data
20063 | 0 | \x726f6f743a783a303a303a726f6f743a2f726f6f743a2f62696e2f626173680a62696e3a783a313a313a62696e3a2f62696e3a2f7362696e2f6e6f6c6f67696e0a6461656d6f6e3a783a323a323a6461656d6f6e3a2f7362696e3a2f7362696e2f6e6f6c6f67696e0a61646d3
a783a333a343a61646d3a2f7661722f61646d3a2f7362696e2f6e6f6c6f67696e0a6c703a783a343a373a6c703a2f7661722f73706f6f6c2f6c70643a2f7362696e2f6e6f6c6f67696e0a73796e633a783a353a303a73796e633a2f7362696e3a2f62696e2f73796e630a73687574646f776e3a783a36
3a303a73687574646f776e3a2f7362696e3a2f7362696e2f73687574646f776e0a68616c743a783a373a303a68616c743a2f7362696e3a2f7362696e2f68616c740a6d61696c3a783a383a31323a6d61696c3a2f7661722f73706f6f6c2f6d61696c3a2f7362696e2f6e6f6c6f67696e0a757563703a7
83a31303a31343a757563703a2f7661722f73706f6f6c2f757563703a2f7362696e2f6e6f6c6f67696e0a6f70657261746f723a783a31313a303a6f70657261746f723a2f726f6f743a2f7362696e2f6e6f6c6f67696e0a67616d65733a783a31323a3130303a67616d65733a2f7573722f67616d6573
3a2f7362696e2f6e6f6c6f67696e0a676f706865723a783a31333a33303a676f706865723a2f7661722f676f706865723a2f7362696e2f6e6f6c6f67696e0a6674703a783a31343a35303a46545020557365723a2f7661722f6674703a2f7362696e2f6e6f6c6f67696e0a6e6f626f64793a783a39393
a39393a4e6f626f64793a2f3a2f7362696e2f6e6f6c6f67696e0a646275733a783a38313a38313a53797374656d206d657373616765206275733a2f3a2f7362696e2f6e6f6c6f67696e0a766373613a783a36393a36393a7669727475616c20636f6e736f6c65206d656d6f7279206f776e65723a2f64
65763a2f7362696e2f6e6f6c6f67696e0a7361736c617574683a783a3439393a37363a225361736c61757468642075736572223a2f7661722f656d7074792f7361736c617574683a2f7362696e2f6e6f6c6f67696e0a706f73746669783a783a38393a38393a3a2f7661722f73706f6f6c2f706f73746
669783a2f7362696e2f6e6f6c6f67696e0a61766168693a783a37303a37303a4176616869206d444e532f444e532d534420537461636b3a2f7661722f72756e2f61766168692d6461656d6f6e3a2f7362696e2f6e6f6c6f67696e0a737368643a783a37343a37343a50726976696c6567652d73657061
7261746564205353483a2f7661722f656d7074792f737368643a2f7362696e2f6e6f6c6f67696e0a706f7374677265733a783a3530303a3530303a3a2f686f6d652f706f7374677265733a2f62696e2f626173680a6170616368653a783a34383a34383a4170616368653a2f7661722f7777773a2f736
2696e2f6e6f6c6f67696e0a7a61626269783a783a3530313a3530313a3a2f686f6d652f7a61626269783a2f62696e2f626173680a
(1 row)
--批量删除
db_big=# insert into tab_big values('passwd list',lo_import('/home/postgres/pg_log/postgresql-2014-01-09_000000.csv',888));
INSERT 0 1
db_big=# select lo_unlink(oid) from pg_largeobject_Metadata where oid in(20063,888) ;
lo_unlink
-----------
1
1
(2 rows)
5.客户端的使用
db_big=# \lo_list
Large objects
ID | Owner | Description
-----+----------+-------------
888 | postgres |
(1 row)
db_big=# \lo_export 888 '/home/postgres/123.txt'
lo_export
db_big=# \lo_import '/home/postgres/123.txt' 'Kenyon_bigdata'
lo_import 20066
db_big=# \lo_list
Large objects
ID | Owner | Description
-------+----------+----------------
888 | postgres |
20066 | postgres | Kenyon_bigdata
(2 rows)
db_big=# \lo_unlink 888
lo_unlink 888
6.权限
a.超级用户使用以上命令都是正常的
b.导出时数据库用户需要有相关的创建文件的权限
三.其他
通常程序或者一些开源工具(比如cas等)在删除用户表时并不会将系统表(pg_largeobject和pg_largeobject_Metadata)删除，或者创建类似的表时不会创建同步的trigger，需要DBA维护一下，否则会导致系统的大对象表越来越大。
四.参考 1.http://www.postgresql.org/docs/9.3/static/catalog-pg-largeobject.html 2.http://giswiki.hsr.ch/Postgresql_-_Binary_Large_Objects 3.http://my.oschina.net/Kenyon/blog/113026
原文链接：https://www.f2er.com/postgresql/195901.html