案例现象：
KingbaseES V8R6集群备库启动后，加入集群失败，sys_log日志信息提示，如下图所示：
适用版本：
kingbaseES V8R6
一、问题分析
在timeline对应的history文件中会记录每次timeline切换时所对应的lsn，如下图所示，在sys_wal目录下：
.......
-rw------- 1 kingbase kingbase 1.2K Feb 21 09:44 0000001B.history
-rw------- 1 kingbase kingbase 1.2K Feb 21 09:44 0000001C.history
-rw------- 1 kingbase kingbase 1.2K Feb 21 09:44 0000001D.history
.....
查看timelinehistory文件的信息：
如下所示，history文件最左列显示timeline_id，第二列显示timeline切换时对应的lsn。
[kingbase@node102 sys_wal]$ cat 0000001D.history
.......
24 4/4D0000A0 no recovery target specified
25 4/51001D00 no recovery target specified
26 4/520000A0 no recovery target specified
27 4/540000A0 no recovery target specified
28 4/580000A0 no recovery target specified
二、问题解决
备库启动数据库服务时，读取控制文件，从检查点对应的lsn开始，执行recovery，一直读取到到当前数据库最大timeline所对应的wal日志，完成数据的一致性恢复，启动实例。
从备库sys_log日志信息看，timeline（29）history文件记录的lsn满足不了数据库的recovery，备库timeline（29）对应的history文件是“0000001D.history”（1D（16）=29（10）），可以将此timeline对应的history文件改名或删除，再重启备库数据库服务连接集群主库。
三、备库recovery过程
1、查看备库checkpiont信息
[kingbase@node102 bin]$ ./sys_controldata -D /data/kingbase/r6ha/data/
sys_control version number: 1201
Catalog version number: 202112261
Database system identifier: 7080367334319169673
Database cluster state: in archive recovery
sys_control last modified: Wed 01 Mar 2023 11:30:13 AM CST
Latest checkpoint location: 6/7F019F30
Latest checkpoint's REDO location: 6/7F019F00 #recovery起始lsn
Latest checkpoint's REDO WAL file: 00000031000000060000007F
2、查看备库启动后sys_log日志
2023-03-01 11:30:13.814 CST,,,2220,,63fec6c4.8ac,3,,2023-03-01 11:30:12 CST,,0,LOG,00000,"entering standby mode",,,,,,,,,""
2023-03-01 11:30:13.814 CST,,,2220,,63fec6c4.8ac,4,,2023-03-01 11:30:12 CST,,0,DEBUG,00000,"backup time 2023-03-01 11:30:11 CST in file ""backup_label""",,,,,,,,,""
2023-03-01 11:30:13.815 CST,,,2220,,63fec6c4.8ac,5,,2023-03-01 11:30:12 CST,,0,DEBUG,00000,"checkpoint record is at 6/7F019F30",,,,,,,,,""
2023-03-01 11:30:13.815 CST,,,2220,,63fec6c4.8ac,6,,2023-03-01 11:30:12 CST,,0,DEBUG,00000,"redo record is at 6/7F019F00; shutdown false",,,,,,,,,""
2023-03-01 11:30:13.818 CST,,,2220,,63fec6c4.8ac,19,,2023-03-01 11:30:12 CST,1/0,0,LOG,00000,"redo starts at 6/7F019F00",,,,,,,,,""
......
2023-03-01 11:31:49.379 CST,,,2220,,63fec6c4.8ac,10240281,,2023-03-01 11:30:12 CST,1/0,0,LOG,00000,"consistent recovery state reached at 6/AB19B9F0",,,,,,,,,""
如下图所示：
3、查看恢复完成对应的wal日志
Tips：
recovery完成时的timeline是31（16进制）（timeline=49），对应的wai日志文件0000003100000006000000AB。
-rw------- 1 kingbase kingbase 16M Mar 1 11:30 0000003100000006000000A9
-rw------- 1 kingbase kingbase 16M Mar 1 11:30 0000003100000006000000AA
-rw------- 1 kingbase kingbase 16M Mar 1 11:36 0000003100000006000000AB
-rw------- 1 kingbase kingbase 2.1K Mar 1 11:30 00000031.history
查看timeline对应history文件：
[kingbase@node102 sys_wal]$ cat 00000031.history
1 0/690000A0 no recovery target specified
2 0/6A0000A0 no recovery target specified
3 1/C50089F0 no recovery target specified
......
47 6/790014E8 no recovery target specified
48 6/7A0000A0 no recovery target specified
查看当前timeline：
prod=# select timeline_id from sys_control_checkpoint();
timeline_id
-------------
49
(1 row)
---如上所示，备库在启动数据库服务后，读取控制文件获取到检查点对应lsn后，开始应用wal日志，直到应用到最新的timeline所对应的wal日志文件达到数据一致性后，停止恢复。