测试前题：
测试cassandra集群使用了vnodes，如何判断是否用了vnodes呢？ 主要看你的cassandra.yml配置文件中。
默认（3.x）为空，系统自动生成。为空表示使用virtual nodes，默认开启，使用了vnodes，删除了节点之后它会自己均衡数据，需要人为干预。
测试数据生成
创建一个名为kevin_test的KeySpace
创建一个名为kevin_test的KeySpace,使用网络拓扑策略(SimpleStrategy),集群内3副本，另外开启写commit log。
cassandra@cqlsh> create keyspace kevin_test with replication = {'class':'SimpleStrategy','replication_factor':3} and durable_writes = true;创建表
CREATE TABLE t_users (
user_id text PRIMARY KEY,
first_name text,
last_name text,
emails set<text>
);批量插入数据
BEGIN BATCH
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('0', 'kevin0', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('1', 'kevin1', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('2', 'kevin2', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('3', 'kevin3', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('4', 'kevin4', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('5', 'kevin5', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('6', 'kevin6', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('7', 'kevin7', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('8', 'kevin8', 'kang', {'[email protected]', '[email protected]'});
INSERT INTO t_users (user_id, first_name, last_name, emails) VALUES('9', 'kevin9', 'kang', {'[email protected]', '[email protected]'});
APPLY BATCH;验证：
cassandra@cqlsh:kevin_test> SELECT * from t_users;
user_id | emails | first_name | last_name
---------+---------------------------------+------------+-----------
6 | {'[email protected]', '[email protected]'} | kevin6 | kang
7 | {'[email protected]', '[email protected]'} | kevin7 | kang
9 | {'[email protected]', '[email protected]'} | kevin9 | kang
4 | {'[email protected]', '[email protected]'} | kevin4 | kang
3 | {'[email protected]', '[email protected]'} | kevin3 | kang
5 | {'[email protected]', '[email protected]'} | kevin5 | kang
0 | {'[email protected]', '[email protected]'} | kevin0 | kang
8 | {'[email protected]', '[email protected]'} | kevin8 | kang
2 | {'[email protected]', '[email protected]'} | kevin2 | kang
1 | {'[email protected]', '[email protected]'} | kevin1 | kang
查看t_users表属性：
[root@kubm-03 ~]# nodetool cfstats kevin_test.t_users
Total number of tables: 41
----------------
Keyspace : kevin_test
Read Count: 0
Read Latency: NaN ms
Write Count: 6
Write Latency: 0.116 ms
Pending Flushes: 0
Table: t_users
Number of partitions (estimate): 5
Memtable cell count: 6
Memtable data size: 828以上表信息，在后期测试期间可以确认数据是否丢失。
集群节点信息
[root@kubm-03 ~]# nodetool status
Datacenter: dc1
===============
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns Host ID Rack
UN 172.20.101.164 56.64 MiB 256 ? dcbbad83-fe7c-4580-ade7-aa763b8d2c40 rack1
UN 172.20.101.165 55.44 MiB 256 ? cefe8a3b-918f-463b-8c7d-faab0b9351f9 rack1
UN 172.20.101.166 73.96 MiB 256 ? 88e16e35-50dd-4ee3-aa1a-f10a8c61a3eb rack1
UN 172.20.101.167 55.43 MiB 256 ? 8808aaf7-690c-4f0c-be9b-ce655c1464d4 rack1
UN 172.20.101.160 54.4 MiB 256 ? 57cc39fc-e47b-4c96-b9b0-b004f2b79242 rack1
UN 172.20.101.157 56.05 MiB 256 ? 091ff0dc-415b-48a7-b4ce-e70c84bbfafc rack1
下线一个正常的集群节点
节点运行状态正常，用于压缩集群节点数量，本次下线：172.20.101.165。
在要删除的机器（172.20.101.165）上执行:
nodetool decommission 或者 nodetool removenode
可以通过 nodetool status查看集群状态，节点数据恢复完成后，下线节点从集群列表消失。
查看服务状态：
[root@kubm-03 ~]# /etc/init.d/cassandra status
● cassandra.service - LSB: distributed storage system for structured data
Loaded: loaded (/etc/rc.d/init.d/cassandra; bad; vendor preset: disabled)
Active: active (running) since Tue 2019-07-09 11:29:25 CST; 2 days ago
Jul 09 11:29:25 kubm-03 cassandra[8495]: Starting Cassandra: OK
Jul 09 11:29:25 kubm-03 systemd[1]: Started LSB: distributed storage system for structured data.测试重启服务，节点能否自动加入集群：
/etc/init.d/cassandra restart
INFO [main] 2019-07-11 16:44:49,765 StorageService.java:639 - CQL supported versions: 3.4.4 (default: 3.4.4)
INFO [main] 2019-07-11 16:44:49,765 StorageService.java:641 - Native protocol supported versions: 3/v3, 4/v4, 5/v5-beta (default: 4/v4)
INFO [main] 2019-07-11 16:44:49,816 IndexSummaryManager.java:80 - Initializing index summary manager with a memory pool size of 198 MB and a resize interval of 60 minutes
This node was decommissioned and will not rejoin the ring unless cassandra.override_decommission=true has been set, or all existing data is removed and the node is bootstrapped again
Fatal configuration error; unable to start server. See log for stacktrace.
ERROR [main] 2019-07-11 16:44:49,823 CassandraDaemon.java:749 - Fatal configuration error
#提示节点已经退役
org.apache.cassandra.exceptions.ConfigurationException: This node was decommissioned and will not rejoin the ring unless cassandra.override_decommission=true has been set, or all existing data is removed and the node is bootstrapped again
#提示节点已经退役，无法接入集群，如果想加入修改修改集群配置 cassandra.override_decommission=true或者删除现在节点上所有数据后重启服务。