CF里面在讨论是否要添加一个查看数据库system id的函数, pg_system_identifier();
这个函数的用途和pg_controldata输出的Database system identifier值其实是一个效果.
只是它的目的是可以用SQL来得到这个值.
看到后面发现一个很有趣的东西,
Fujii Masao回复的如下 :
BTW, you can see the system identifier by executing IDENTIFY_SYSTEM
command in replication connection as follows:
1. Change the server settings so that the server can accept the
replication connection
2. Connect to the server in replication mode
3. Execute IDENTIFY_SYSTEM command in replication connection
$ psql "replication=1"
=# IDENTIFY_SYSTEM;
systemid | timeline | xlogpos
---------------------+----------+-----------
5914930202950905854 | 1 | 0/183F720
(1 row)
This is not good way for a user, though ;P
> I don't know if that's justification enough, which is
> why I didn't add it to the commitfest yet.
You can add the patch to CF, and then hear the opinions from other people
during CF.
Regards,
--
Fujii Masao
原来还可以这么玩, 于是乎找了一个测试库试一试.
172.16.3.33 主库 (host replication postgres 172.16.3.0/24 md5)
172.16.3.39 备库
在172.16.3.39上以standby角色去连接172.16.3.33的主库.
得到的值和 pg_controldata一致.
pg94@db-172-16-3-39-> psql "replication=1" -h 172.16.3.33 -U postgres
Password for user postgres:
psql (9.4devel)
Type "help" for help.
digoal=#
digoal=# IDENTIFY_SYSTEM;
systemid | timeline | xlogpos
---------------------+----------+------------
5912195073286594075 | 1 | 6/80000668
(1 row)得到的值和 pg_controldata一致.
pg94@db-172-16-3-33-> pg_controldata |grep identifier
Database system identifier: 5912195073286594075
Maximum length of identifiers: 64
除了使用
IDENTIFY_SYSTEM, replication protocol还支持其他的命令.
详见 :
http://www.postgresql.org/docs/devel/static/protocol-replication.html
IDENTIFY_SYSTEM
TIMELINE_HISTORY tli
START_REPLICATION XXX/XXX TIMELINE tli
BASE_BACKUP [LABEL 'label'] [PROGRESS] [FAST] [WAL] [NOWAIT]
包括pg_basebackup , 也是使用流复制协议进行数据复制的.
另外几个命令也可以在psql命令行中使用, 例如 :
在主节点pg_xlog中创建一个history文件.
其他命令 :
[参考]
[root@db-172-16-3-33 pg_basebackup]# su - pg94
pg94@db-172-16-3-33-> cd $PGDATA
pg94@db-172-16-3-33-> vi pg_xlog/00000002.history
test line 1
test line 2
使用流复制命令接收history文件内容.
digoal=# TIMELINE_HISTORY 2;
filename | content
------------------+-------------
00000002.history | test line 1+
| test line 2+
|
(1 row)其他命令 :
digoal=# select * from pg_current_xlog_location();
pg_current_xlog_location
--------------------------
6/800007A8
(1 row)digoal=# START_REPLICATION 6/80000700 TIMELINE 1;
unexpected PQresultStatus: 8
digoal=# START_REPLICATION 6/80000700 TIMELINE 1;
PQexec not allowed during COPY BOTH
BASE_BACKUP 是做基础备份的, 数据比较庞大.
1. src/backend/replication/repl_gram.y
3.
http://www.postgresql.org/message-id/flat/5215346B.7070800@dalibo.com#5215346B.7070800@dalibo.com
4. src/interfaces/libpq/libpq-int.h
/*
* PGconn stores all the state data associated with a single connection
* to a backend.
*/
struct pg_conn
{
/* Saved values of connection options */
char *pghost; /* the machine on which the server is running */
char *pghostaddr; /* the numeric IP address of the machine on
* which the server is running. Takes
* precedence over above. */
char *pgport; /* the server's communication port */
char *pgunixsocket; /* the Unix-domain socket that the server is
* listening on; if NULL, uses a default
* constructed from pgport */
char *pgtty; /* tty on which the backend messages is
* displayed (OBSOLETE, NOT USED) */
char *connect_timeout; /* connection timeout (numeric string) */
char *client_encoding_initial; /* encoding to use */
char *pgoptions; /* options to start the backend with */
char *appname; /* application name */
char *fbappname; /* fallback application name */
char *dbName; /* database name */
char *replication; /* connect as the replication standby? */
replication指定是否以standby连接到主库.
... 其他略.
