kingbaseES V8R6集群运维案例之---max_connections参数修改
案例说明：
数据库max_connections指定了数据库的最大连接数，对于集群部署后默认值是100，生产环境可以根据需要调整，但是注意：
适用版本：
KingbaseES V8R6
1、查看主备库原始max_connections配置
[kingbase@node1 data]$ cat kingbase.conf |grep max_con
max_connections = 1000 # (change requires restart)
[kingbase@node1 data]$ cat es_rep.conf |grep max_conn
max_connections='100'
[kingbase@node3 data]$ cat kingbase.conf |grep max_con
max_connections = 1000 # (change requires restart)
[kingbase@node3 data]$ cat es_rep.conf |grep max_conn
max_connections='100'
2、修改主备库max_connections参数（小于原始max_connections参数值）
[kingbase@node3 data]$ cat kingbase.conf|grep -i max_conn
max_connections = 500 # (change requires restart)
[kingbase@node3 data]$ cat es_rep.conf|grep -i max_conn
max_connections='100'
[kingbase@node1 data]$ cat kingbase.conf |grep max_conn
max_connections = 500 # (change requires restart)
[kingbase@node1 data]$ cat es_rep.conf |grep max_conn
max_connections='100'
3、启动主备库数据库服务
=备库启动失败，故障信息“because max_connections = 500 is a lower setting than on the master server (its value was 1000)”=
启动主库：
[kingbase@node1 bin]$ ./sys_ctl start -D ../data
waiting for server to start....2021-03-01 18:19:20.719 CST [6681] LOG: sepapower extension initialized
2021-03-01 18:19:20.720 CST [6681] LOG: starting KingbaseES V008R006C003B0010 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit
2021-03-01 18:19:20.720 CST [6681] LOG: listening on IPv4 address "0.0.0.0", port 54321
2021-03-01 18:19:20.720 CST [6681] LOG: listening on IPv6 address "::", port 54321
2021-03-01 18:19:20.862 CST [6681] LOG: listening on Unix socket "/tmp/.s.KINGBASE.54321"
2021-03-01 18:19:21.034 CST [6681] LOG: redirecting log output to logging collector process
2021-03-01 18:19:21.034 CST [6681] HINT: Future log output will appear in directory "sys_log".
done
server started
[kingbase@node1 bin]$ ./ksql -U system test
ksql (V8.0)
Type "help" for help.
test=# show max_connections ;
max_connections
-----------------
500
(1 row)
启动备库：
[kingbase@node3 bin]$ ./sys_ctl start -D ../data
waiting for server to start....2021-03-01 18:19:36.475 CST [9569] LOG: sepapower extension initialized
2021-03-01 18:19:36.476 CST [9569] LOG: starting KingbaseES V008R006C003B0010 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit
2021-03-01 18:19:36.477 CST [9569] LOG: listening on IPv4 address "0.0.0.0", port 54321
2021-03-01 18:19:36.477 CST [9569] LOG: listening on IPv6 address "::", port 54321
2021-03-01 18:19:36.489 CST [9569] LOG: listening on Unix socket "/tmp/.s.KINGBASE.54321"
2021-03-01 18:19:36.515 CST [9569] LOG: redirecting log output to logging collector process
2021-03-01 18:19:36.515 CST [9569] HINT: Future log output will appear in directory "sys_log".
. stopped waiting
sys_ctl: could not start server
Examine the log output.
[kingbase@node3 sys_log]$ tail -100 kingbase-2021-03-01_181936.log
2021-03-01 18:19:36.518 CST [9571] LOG: database system was interrupted while in recovery at log time 2021-03-01 18:13:49 CST
2021-03-01 18:19:36.518 CST [9571] HINT: If this has occurred more than once some data might be corrupted and you might need to choose an earlier recovery target.
2021-03-01 18:19:37.585 CST [9571] LOG: entering standby mode
2021-03-01 18:19:37.631 CST [9571] FATAL: hot standby is not possible because max_connections = 500 is a lower setting than on the master server (its value was 1000)
2021-03-01 18:19:37.633 CST [9569] LOG: startup process (PID 9571) exited with exit code 1
2021-03-01 18:19:37.633 CST [9569] LOG: aborting startup due to startup process failure
2021-03-01 18:19:37.640 CST [9569] LOG: database system is shut down
4、修改备库max_connections参数配置并启动数据库
[kingbase@node3 data]$ cat kingbase.conf|grep -i max_conn
max_connections = 1000 # (change requires restart)
You have mail in /var/spool/mail/kingbase
[kingbase@node3 data]$ cat es_rep.conf|grep -i max_conn
max_connections='100'
[kingbase@node3 bin]$ ./sys_ctl start -D ../data
waiting for server to start....2021-03-01 18:20:42.606 CST [9667] LOG: sepapower extension initialized
2021-03-01 18:20:42.607 CST [9667] LOG: starting KingbaseES V008R006C003B0010 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit
2021-03-01 18:20:42.607 CST [9667] LOG: listening on IPv4 address "0.0.0.0", port 54321
2021-03-01 18:20:42.607 CST [9667] LOG: listening on IPv6 address "::", port 54321
2021-03-01 18:20:42.636 CST [9667] LOG: listening on Unix socket "/tmp/.s.KINGBASE.54321"
2021-03-01 18:20:42.679 CST [9667] LOG: redirecting log output to logging collector process
2021-03-01 18:20:42.679 CST [9667] HINT: Future log output will appear in directory "sys_log".
done
server started
[kingbase@node3 bin]$ ps -ef |grep kingbase
kingbase 9667 1 0 18:20 ? 00:00:00 /home/kingbase/cluster/R6HA/KHA/kingbase/bin/kingbase -D ../data
kingbase 9668 9667 0 18:20 ? 00:00:00 kingbase: logger
kingbase 9669 9667 3 18:20 ? 00:00:00 kingbase: startup recovering 0000000E00000004000000AB
kingbase 9670 9667 0 18:20 ? 00:00:00 kingbase: checkpointer
kingbase 9671 9667 0 18:20 ? 00:00:00 kingbase: background writer
kingbase 9672 9667 0 18:20 ? 00:00:00 kingbase: stats collector
kingbase 9673 9667 0 18:20 ? 00:00:00 kingbase: walreceiver streaming 4/AB000110
5、重启集群测试
[kingbase@node3 bin]$ ./sys_monitor.sh restart
2021-03-01 18:23:06 Ready to stop all DB ...
.......
2021-03-01 18:23:47 repmgrd on "[192.168.7.243]" start success.
ID | Name | Role | Status | Upstream | repmgrd | PID | Paused? | Upstream last seen
----+---------+---------+-----------+----------+---------+-------+---------+--------------------
1 | node248 | primary | * running | | running | 9290 | no | n/a
3 | node243 | standby | running | node248 | running | 11332 | no | 0 second(s) ago
2021-03-01 18:23:54 Done.
---如上所示，集群启动正常。
