Segment检测及故障切换机制
GP Master首先会检测Primary状态，如果Primary不可连通，那么将会检测Mirror状态，Primary/Mirror状态总共有4种：
- Primary活着，Mirror活着。GP Master探测Primary成功之后直接返回，进行下一个Segment检测；
- Primary活着，Mirror挂了。GP Master探测Primary成功之后，通过Primary返回的状态得知Mirror挂掉了（Mirror挂掉之后，Primary将会探测到，将自己变成ChangeTracking模式），这时候更新Master元信息，进行下一个Segment检测；
- Primary挂了，Mirror活着。GP Master探测Primary失败之后探测Mirror，发现Mirror是活着，这时候更新Master上面的元信息，同时使Mirror接管Primary（故障切换），进行下一个Segment检测；
- Primary挂了，Mirror挂了。GP Master探测Primary失败之后探测Mirror，Mirror也是挂了，直到重试最大值，结束这个Segment的探测，也不更新Master元信息了，进行下一个Segment检测。
上面的2-4需要进行gprecoverseg进行segment恢复。
对失败的segment节点；启动时会直接跳过，忽略。
[gpadmin@mdw ~]$ gpstart
==≥ gpstart:mdw:gpadmin-[INFO]:-Starting gpstart with args:
==≥ gpstart:mdw:gpadmin-[INFO]:-Gathering information and validating the environment...
==≥ gpstart:mdw:gpadmin-[INFO]:-Greenplum Binary Version: 'postgres (Greenplum Database) 5.0.0 build 1'
==≥ 。。。。。。。。。。。。。。。。。。。。。。。。。。
==≥ gpstart:mdw:gpadmin-[INFO]:-Master Started...
==≥ gpstart:mdw:gpadmin-[INFO]:-Shutting down master
==≥ gpstart:mdw:gpadmin-[WARNING]:-Skipping startup of segment marked down in configuration: on sdw2 directory /data/gpdata/gpdatam/gpseg0 <<<<<
==≥ gpstart:mdw:gpadmin-[INFO]:---------------------------
==≥ gpstart:mdw:gpadmin-[INFO]:-Master instance parameters
==≥ gpstart:mdw:gpadmin-[INFO]:---------------------------
==≥ gpstart:mdw:gpadmin-[INFO]:-Database = template1
==≥ gpstart:mdw:gpadmin-[INFO]:-Master Port = 1921
==≥ gpstart:mdw:gpadmin-[INFO]:-Master directory = /data/gpdata/pgmaster/gpseg-1
==≥ gpstart:mdw:gpadmin-[INFO]:-Timeout = 600 seconds
==≥ gpstart:mdw:gpadmin-[INFO]:-Master standby = Off
==≥ gpstart:mdw:gpadmin-[INFO]:---------------------------------------
==≥ gpstart:mdw:gpadmin-[INFO]:-Segment instances that will be started
==≥ gpstart:mdw:gpadmin-[INFO]:---------------------------------------
==≥ gpstart:mdw:gpadmin-[INFO]:- Host Datadir Port Role
==≥ gpstart:mdw:gpadmin-[INFO]:- sdw1 /data/gpdata/gpdatap/gpseg0 40000 Primary
==≥ gpstart:mdw:gpadmin-[INFO]:- sdw2 /data/gpdata/gpdatap/gpseg1 40000 Primary
==≥ gpstart:mdw:gpadmin-[INFO]:- sdw1 /data/gpdata/gpdatam/gpseg1 50000 Mirror
Continue with Greenplum instance startup Yy|Nn (default=N):
> y
==》gpstart:mdw:gpadmin-[INFO]:-Commencing parallel primary and mirror segment instance startup, please wait...
==》
==》gpstart:mdw:gpadmin-[INFO]:-Process results...
==》gpstart:mdw:gpadmin-[INFO]:-----------------------------------------------------
==》gpstart:mdw:gpadmin-[INFO]:- Successful segment starts = 3
==》gpstart:mdw:gpadmin-[INFO]:- Failed segment starts = 0
==》gpstart:mdw:gpadmin-[WARNING]:-Skipped segment starts (segments are marked down in configuration) = 1 <<<<<<<<
==》gpstart:mdw:gpadmin-[INFO]:-----------------------------------------------------
==》gpstart:mdw:gpadmin-[INFO]:-
==》gpstart:mdw:gpadmin-[INFO]:-Successfully started 3 of 3 segment instances, skipped 1 other segments
==》gpstart:mdw:gpadmin-[INFO]:-----------------------------------------------------
==》gpstart:mdw:gpadmin-[WARNING]:-****************************************************************************
==》gpstart:mdw:gpadmin-[WARNING]:-There are 1 segment(s) marked down in the database
==》gpstart:mdw:gpadmin-[WARNING]:-To recover from this current state, review usage of the gprecoverseg
==》gpstart:mdw:gpadmin-[WARNING]:-management utility which will recover failed segment instance databases.
==》gpstart:mdw:gpadmin-[WARNING]:-****************************************************************************
==》gpstart:mdw:gpadmin-[INFO]:-Starting Master instance mdw directory /data/gpdata/pgmaster/gpseg-1
==》gpstart:mdw:gpadmin-[INFO]:-Command pg_ctl reports Master mdw instance active
==》gpstart:mdw:gpadmin-[INFO]:-No standby master configured. skipping...
==》gpstart:mdw:gpadmin-[WARNING]:-Number of segments not attempted to start: 1
==》gpstart:mdw:gpadmin-[INFO]:-Check status of database with gpstate utility51
查看数据库的mirror的节点启动状态
[gpadmin@mdw ~]$ gpstate -m
==》gpstate:mdw:gpadmin-[INFO]:-Starting gpstate with args: -m
==》gpstate:mdw:gpadmin-[INFO]:-local Greenplum Version: 'postgres (Greenplum Database) 5.0.0 build 1'
==》gpstate:mdw:gpadmin-[INFO]:-master Greenplum Version: 'PostgreSQL 8.3.23 (Greenplum Database 5.0.0 build 1)
==》gpstate:mdw:gpadmin-[INFO]:-Obtaining Segment details from master...
==》gpstate:mdw:gpadmin-[INFO]:--------------------------------------------------------------
==》gpstate:mdw:gpadmin-[INFO]:--Current GPDB mirror list and status
==》gpstate:mdw:gpadmin-[INFO]:--Type = Spread
==》gpstate:mdw:gpadmin-[INFO]:--------------------------------------------------------------
==》gpstate:mdw:gpadmin-[INFO]:- Mirror Datadir Port Status Data Status
==》gpstate:mdw:gpadmin-[WARNING]:-sdw2 /data/gpdata/gpdatam/gpseg0 50000 Failed <<<<<<<<
==》gpstate:mdw:gpadmin-[INFO]:- sdw1 /data/gpdata/gpdatam/gpseg1 50000 Passive Synchronized
==》gpstate:mdw:gpadmin-[INFO]:--------------------------------------------------------------
==》gpstate:mdw:gpadmin-[WARNING]:-1 segment(s) configured as mirror(s) have failed
可直观看出“[WARNING]:-sdw2 /data/gpdata/gpdatam/gpseg0 50000 Failed ”
如何恢复这个mirror segment呢？
首先产生一个恢复的配置文件 ： gprecoverseg -o ./recov
---- 当然primary segment也是这样恢复 ----
[gpadmin@mdw ~]$ gprecoverseg -o ./recov
==》gprecoverseg:mdw:gpadmin-[INFO]:-Starting gprecoverseg with args: -o ./recov
==》gprecoverseg:mdw:gpadmin-[INFO]:-local Greenplum Version: 'postgres (Greenplum Database) 5.0.0 build 1'
==》gprecoverseg:mdw:gpadmin-[INFO]:-master Greenplum Version: 'PostgreSQL 8.3.23 (Greenplum Database 5.0.0 build 1) on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.4.2 compiled on ==》
==》gprecoverseg:mdw:gpadmin-[INFO]:-Checking if segments are ready
==》gprecoverseg:mdw:gpadmin-[INFO]:-Obtaining Segment details from master...
==》gprecoverseg:mdw:gpadmin-[INFO]:-Obtaining Segment details from master...
==》gprecoverseg:mdw:gpadmin-[INFO]:-Configuration file output to ./recov successfully.
查看恢复的配置文件
可以知道哪些segment需要恢复
[gpadmin@mdw ~]$ cat recov
filespaceOrder=fastdisk
sdw2:50000:/data/gpdata/gpdatam/gpseg03
使用配置文件进行恢复 ：
[gpadmin@mdw ~]$ gprecoverseg -i ./recov
==》gprecoverseg:mdw:gpadmin-[INFO]:-Starting gprecoverseg with args: -i ./recov
==》gprecoverseg:mdw:gpadmin-[INFO]:-local Greenplum Version: 'postgres (Greenplum Database) 5.0.0 build 1'
==》gprecoverseg:mdw:gpadmin-[INFO]:-master Greenplum Version: 'PostgreSQL 8.3.23 (Greenplum Database 5.0.0 build 1) on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.4.2 compiled on ==》
==》gprecoverseg:mdw:gpadmin-[INFO]:-Checking if segments are ready
==》gprecoverseg:mdw:gpadmin-[INFO]:-Obtaining Segment details from master...
==》gprecoverseg:mdw:gpadmin-[INFO]:-Obtaining Segment details from master...
==》gprecoverseg:mdw:gpadmin-[INFO]:-Greenplum instance recovery parameters
==》gprecoverseg:mdw:gpadmin-[INFO]:----------------------------------------------------------
==》gprecoverseg:mdw:gpadmin-[INFO]:-Recovery from configuration -i option supplied
==》gprecoverseg:mdw:gpadmin-[INFO]:----------------------------------------------------------
==》gprecoverseg:mdw:gpadmin-[INFO]:-Recovery 1 of 1
==》gprecoverseg:mdw:gpadmin-[INFO]:----------------------------------------------------------
==》gprecoverseg:mdw:gpadmin-[INFO]:- Synchronization mode = Incremental
==》gprecoverseg:mdw:gpadmin-[INFO]:- Failed instance host = sdw2
==》gprecoverseg:mdw:gpadmin-[INFO]:- Failed instance address = sdw2
==》gprecoverseg:mdw:gpadmin-[INFO]:- Failed instance directory = /data/gpdata/gpdatam/gpseg0
==》gprecoverseg:mdw:gpadmin-[INFO]:- Failed instance port = 50000
==》gprecoverseg:mdw:gpadmin-[INFO]:- Failed instance replication port = 51000
==》gprecoverseg:mdw:gpadmin-[INFO]:- Failed instance fastdisk directory = /data/gpdata/seg1/pg_mir_cdr/gpseg0
==》gprecoverseg:mdw:gpadmin-[INFO]:- Recovery Source instance host = sdw1
==》gprecoverseg:mdw:gpadmin-[INFO]:- Recovery Source instance address = sdw1
==》gprecoverseg:mdw:gpadmin-[INFO]:- Recovery Source instance directory = /data/gpdata/gpdatap/gpseg0
==》gprecoverseg:mdw:gpadmin-[INFO]:- Recovery Source instance port = 40000
==》gprecoverseg:mdw:gpadmin-[INFO]:- Recovery Source instance replication port = 41000
==》gprecoverseg:mdw:gpadmin-[INFO]:- Recovery Source instance fastdisk directory = /data/gpdata/seg1/pg_pri_cdr/gpseg0
==》gprecoverseg:mdw:gpadmin-[INFO]:- Recovery Target = in-place
==》gprecoverseg:mdw:gpadmin-[INFO]:-Process results...
==》gprecoverseg:mdw:gpadmin-[INFO]:-Done updating primaries
==》gprecoverseg:mdw:gpadmin-[INFO]:-******************************************************************
==》gprecoverseg:mdw:gpadmin-[INFO]:-Updating segments for resynchronization is completed.
==》gprecoverseg:mdw:gpadmin-[INFO]:-For segments updated successfully, resynchronization will continue in the background.
==》gprecoverseg:mdw:gpadmin-[INFO]:-
==》gprecoverseg:mdw:gpadmin-[INFO]:-Use gpstate -s to check the resynchronization progress.
==》gprecoverseg:mdw:gpadmin-[INFO]:-******************************************************************35
查看恢复状态
[gpadmin@mdw ~]$ gpstate -m
==》gpstate:mdw:gpadmin-[INFO]:-Starting gpstate with args: -m
==》gpstate:mdw:gpadmin-[INFO]:-local Greenplum Version: 'postgres (Greenplum Database) 5.0.0 build 1'
==》。。。。。。。。。。。。。。。。。。。。。。。。。。
==》gpstate:mdw:gpadmin-[INFO]:-Obtaining Segment details from master...
==》gpstate:mdw:gpadmin-[INFO]:--------------------------------------------------------------
==》gpstate:mdw:gpadmin-[INFO]:--Current GPDB mirror list and status
==》gpstate:mdw:gpadmin-[INFO]:--Type = Spread
==》gpstate:mdw:gpadmin-[INFO]:--------------------------------------------------------------
==》gpstate:mdw:gpadmin-[INFO]:- Mirror Datadir Port Status Data Status
==》gpstate:mdw:gpadmin-[INFO]:- sdw2 /data/gpdata/gpdatam/gpseg0 50000 Passive Resynchronizing
==》gpstate:mdw:gpadmin-[INFO]:- sdw1 /data/gpdata/gpdatam/gpseg1 50000 Passive Synchronized
==》gpstate:mdw:gpadmin-[INFO]:--------------------------------------------------------------13
primary mirror角色对调
数据库的主备就恢复了，但是还有一步，是可选的。要不要把primary mirror角色对调一下，因为现在mirror和primary和优先角色是相反的。 如果要对调，使用以下命令，会停库来处理。
gprecoverseg -r
用于修复Segment的是gprecoverseg。使用方式比较简单，几个主要参数如下：
-i ：主要参数，用于指定一个配置文件，该配置文件描述了需要修复的Segment和修复后的目的位置。
-F ：可选项，指定后，gprecoverseg会将”-i”中指定的或标记”d”的实例删除，并从活着的Mirror复制一个完整一份到目标位置。
-r ：当FTS发现有Primary宕机并进行主备切换，在gprecoverseg修复后，担当Primary的Mirror角色并不会立即切换回来，就会导致部分主机上活跃的Segment过多从而引起性能瓶颈。因此需要恢复Segment原先的角色，称为re-balance.
