环境介绍：
Gpdb版本：5.5.0 二进制版本
操作系统版本： CentOS linux 7.0
Master segment: 192.168.1.225/24 hostname: mfsmaster
Stadnby segemnt: 192.168.1.227/24 hostname: server227
Segment 节点1： 192.168.1.227/24 hostname: server227
Segment 节点2： 192.168.1.17/24 hostname: server17
Segment 节点3： 192.168.1.11/24 hostname: server11
每个segment节点上分别运行一个primary segment和一个mirror segment
一、查看原始状态
select * from gp_segment_configuration;
$ gpstate -f
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:-Starting gpstate with args: -f
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:-local Greenplum Version: 'postgres (Greenplum Database) 5.5.0 build commit:67afa18296aa238d53a2dfcc724da60ed2f944f0'
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:-master Greenplum Version: 'PostgreSQL 8.3.23 (Greenplum Database 5.5.0 build commit:67afa18296aa238d53a2dfcc724da60ed2f944f0) on x86_64-pc-linux-gnu, compiled by GCC gcc (GCC) 6.2.0, 64-bit compiled on Feb 17 2018 15:23:55'
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:-Obtaining Segment details from master...
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:-Standby master details
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:-----------------------
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:- Standby address = server227
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:- Standby data directory = /home/gpadmin/master/gpseg-1
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:- Standby port = 5432
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:- Standby PID = 22279
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:- Standby status = Standby host passive
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--------------------------------------------------------------
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--pg_stat_replication
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--------------------------------------------------------------
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--WAL Sender State: streaming
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--Sync state: sync
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--Sent Location: 0/CF2C470
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--Flush Location: 0/CF2C470
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--Replay Location: 0/CF2C470
20180320:13:50:38:021814 gpstate:mfsmaster:gpadmin-[INFO]:--------------------------------------------------------------
二、master主从切换
1、模拟当前主库宕机，这里直接采用killall gpadmin用户下的所有进程来模拟
2、在master standby节点（227服务器上）进行执行切换命令，提升227为master
$ gpactivatestandby -d master/gpseg-1/
20180320:13:53:20:030558 gpactivatestandby:server227:gpadmin-[INFO]:------------------------------------------------------
20180320:13:53:20:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Standby data directory = /home/gpadmin/master/gpseg-1
20180320:13:53:20:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Standby port = 5432
20180320:13:53:20:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Standby running = yes
20180320:13:53:20:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Force standby activation = no
20180320:13:53:20:030558 gpactivatestandby:server227:gpadmin-[INFO]:------------------------------------------------------
Do you want to continue with standby master activation? Yy|Nn (default=N):
> y
20180320:13:53:26:030558 gpactivatestandby:server227:gpadmin-[INFO]:-found standby postmaster process
20180320:13:53:26:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Updating transaction files filespace flat files...
20180320:13:53:26:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Updating temporary files filespace flat files...
20180320:13:53:26:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Promoting standby...
20180320:13:53:26:030558 gpactivatestandby:server227:gpadmin-[DEBUG]:-Waiting for connection...
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Standby master is promoted
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Reading current configuration...
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[DEBUG]:-Connecting to dbname='postgres'
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Writing the gp_dbid file - /home/gpadmin/master/gpseg-1/gp_dbid...
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-But found an already existing file.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Hence removed that existing file.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Creating a new file...
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Wrote dbid: 1 to the file.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Now marking it as read only...
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Verifying the file...
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:------------------------------------------------------
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-The activation of the standby master has completed successfully.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-server227 is now the new primary master.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-You will need to update your user access mechanism to reflect
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-the change of master hostname.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Do not re-start the failed master while the fail-over master is
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-operational, this could result in database corruption!
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-MASTER_DATA_DIRECTORY is now /home/gpadmin/master/gpseg-1 if
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-this has changed as a result of the standby master activation, remember
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-to change this in any startup scripts etc, that may be configured
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-to set this value.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-MASTER_PORT is now 5432, if this has changed, you
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-may need to make additional configuration changes to allow access
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-to the Greenplum instance.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Refer to the Administrator Guide for instructions on how to re-activate
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-the master to its previous state once it becomes available.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-Query planner statistics must be updated on all databases
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-following standby master activation.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:-When convenient, run ANALYZE against all user databases.
20180320:13:53:27:030558 gpactivatestandby:server227:gpadmin-[INFO]:------------------------------------------------------
3、测试提升后的主库是否正常
$ psql -d postgres -c 'ANALYZE'
postgres=# select * from gp_segment_configuration;
4、这里可能需要同步配置一下pg_hba.conf文件，才能通过客户端进行远程连接
到这里我们已经完成了master节点的故障切换工作。