Greenplum 与 PostgreSQL 修改元数据(catalog)的方法 allow_system_table_mods

背景

PostgreSQL大量的信息保存在元数据中，所有的元数据都是内部维护的，例如建表、建索引、删表等操作，自动维护元数据。

在某些迫不得已的情况下才可能需要直接对元数据进行修改。

默认情况下，用户是允许修改元数据的。

postgres=# \set VERBOSITY verbose  

postgres=# delete from pg_class where relname='test';
ERROR:  42809: permission denied: "pg_class" is a system catalog
LOCATION:  setTargetTable, parse_clause.c:802

Greenplum 打开修改元数据开关的方法

postgres=# set allow_system_table_mods='DML';
SET
postgres=# begin;
BEGIN
postgres=# delete from pg_class where relname='test';
DELETE 1
postgres=# rollback;
ROLLBACK

PostgreSQL 打开修改元数据开关的方法

1、与Greenplum不同

postgres=# set allow_system_table_mods='DML';
ERROR:  parameter "allow_system_table_mods" cannot be changed without restarting the server

2、需要重启生效，配置为on, off。

postgres=# alter system set allow_system_table_mods=on;
ALTER SYSTEM  

postgres=# \q
digoal@  -> pg_ctl stop -m fast
waiting for server to shut down....................... done
server stopped  

digoal@  -> pg_ctl start
waiting for server to start....2018-06-24 10:27:04.987 CST [4239] LOG:  00000: listening on IPv4 address "0.0.0.0", port 4000
2018-06-24 10:27:04.987 CST [4239] LOCATION:  StreamServerPort, pqcomm.c:593
2018-06-24 10:27:04.990 CST [4239] LOG:  00000: listening on Unix socket "/tmp/.s.PGSQL.4000"
2018-06-24 10:27:04.990 CST [4239] LOCATION:  StreamServerPort, pqcomm.c:587
2018-06-24 10:27:04.991 CST [4239] LOG:  00000: listening on Unix socket "./.s.PGSQL.4000"
2018-06-24 10:27:04.991 CST [4239] LOCATION:  StreamServerPort, pqcomm.c:587  

..2018-06-24 10:27:06.980 CST [4239] LOG:  00000: redirecting log output to logging collector process
2018-06-24 10:27:06.980 CST [4239] HINT:  Future log output will appear in directory "log".
2018-06-24 10:27:06.980 CST [4239] LOCATION:  SysLogger_Start, syslogger.c:635
 done
server started  

digoal@  -> psql
psql (11beta1)
Type "help" for help.  

postgres=# show allow_system_table_mods;
 allow_system_table_mods
-------------------------
 on
(1 row)  

postgres=# begin;
BEGIN
postgres=# delete from pg_class where relname='test';
DELETE 1
postgres=# rollback;
ROLLBACK
postgres=# \d test
                             Table "public.test"
 Column |  Type  | Collation | Nullable |               Default
--------+--------+-----------+----------+-------------------------------------
 id     | bigint |           |          |
 c1     | text   |           |          | md5((random())::text)
 c2     | text   |           |          | md5((random())::text)
 c3     | text   |           |          | md5((random())::text)
 c4     | text   |           |          | md5((random())::text)
 c5     | text   |           |          | md5((random())::text)

参考

https://www.postgresql.org/docs/10/static/runtime-config-developer.html

转载自：https://yq.aliyun.com/articles/647438