前言
Cassandra 是一款开源分布式数据库软件，可以提供高容错，高性能，高可用，高弹性，可线性扩展的特性
在 CAP 理论中，它很好地实践了 AP 牺牲了 C, 它是一个最终一致性数据库
Cqlsh 是 Cassandra 的客户端
下面分享一下 Cqlsh 的简单使用方法
参考 Cassandra Tools
Tip: 当前版本 Cassandra 3.11.1 和 cqlsh 5.0.1
操作
系统环境
代码语言：javascript复制[root@much ~]# hostnamectl
Static hostname: much
Icon name: computer-vm
Chassis: vm
Machine ID: 33dc28f7e76c4903ad9b603b77e29a7c
Boot ID: f13f6477c2db43f9a7febda448d0468e
Virtualization: kvm
Operating System: CentOS Linux 7 (Core)
CPE OS Name: cpe:/o:centos:centos:7
Kernel: Linux 3.10.0-514.21.1.el7.x86_64
Architecture: x86-64
[root@much ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 08:00:27:f9:30:bb brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global dynamic enp0s3
valid_lft 84011sec preferred_lft 84011sec
inet6 fe80::2bb7:5b3:9584:d8eb/64 scope link
valid_lft forever preferred_lft forever
3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 08:00:27:a1:e7:17 brd ff:ff:ff:ff:ff:ff
inet 192.168.56.210/24 brd 192.168.56.255 scope global enp0s8
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fea1:e717/64 scope link
valid_lft forever preferred_lft forever
4: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN qlen 1000
link/ether 52:54:00:16:5e:11 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
valid_lft forever preferred_lft forever
5: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN qlen 1000
link/ether 52:54:00:16:5e:11 brd ff:ff:ff:ff:ff:ff
[root@much ~]#依赖
- Python 2.7
代码语言：javascript复制For using cqlsh, the latest version of Python 2.7
[root@much ~]# python -V
Python 2.7.5
[root@much ~]#路径
代码语言：javascript复制[root@much ~]# rpm -ql cassandra | grep cqlsh | grep bin
/usr/bin/cqlsh
/usr/bin/cqlsh.py
[root@much ~]#在安装 cassandra 的过程中就已经自带了客户端
连接
代码语言：javascript复制[root@much ~]# cqlsh localhost
Connected to Test Cluster at localhost:9042.
[cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.
cqlsh>默认会连接本地的 9042 号端口
常用命令
CONSISTENCY
获取或设定一致性级别
代码语言：javascript复制cqlsh> CONSISTENCY
Current consistency level is ONE.
cqlsh>有以下几种级别
- ANY
- ONE
- TWO
- THREE
- QUORUM
- ALL
- LOCAL_QUORUM
- LOCAL_ONE
- SERIAL
- LOCAL_SERIAL
SERIAL CONSISTENCY
获取或设定串行一致性级别
代码语言：javascript复制cqlsh> SERIAL CONSISTENCY
Current serial consistency level is SERIAL.
cqlsh>有以下几种级别
- SERIAL
- LOCAL_SERIAL
此串行一致性级别主要用于更新操作
The serial consistency level is only used by conditional updates (INSERT, UPDATE and DELETE with an IF condition)
show VERSION
查看当前版本
代码语言：javascript复制cqlsh> show VERSION
[cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4]
cqlsh>show HOST
查看当前连接的集群主机和端口
代码语言：javascript复制cqlsh> show HOST
Connected to Test Cluster at localhost:9042.
cqlsh>SHOW SESSION
打印出一个 session 的详细内容
代码语言：javascript复制cqlsh> SHOW
HOST SESSION VERSION
cqlsh> SHOW SESSION
Improper SHOW command.
cqlsh> SHOW SESSION 95ac6470-327e-11e6-beca-dfb660d92ad8
Session 95ac6470-327e-11e6-beca-dfb660d92ad8 wasn't found.
cqlsh>SOURCE
执行指定文件中的 CQL 语句集
代码语言：javascript复制[root@much ~]# echo 'SHOW VERSION' > abc.cql
[root@much ~]# cat abc.cql
SHOW VERSION
[root@much ~]# cqlsh localhost
Connected to Test Cluster at localhost:9042.
[cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.
cqlsh> SOURCE '~/abc.cql'
[cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4]
cqlsh>CAPTURE
抓取查询结果
特殊命令的输出将不会被抓取
代码语言：javascript复制[root@much ~]# > abc.log
[root@much ~]# cat abc.log
[root@much ~]# cqlsh localhost
Connected to Test Cluster at localhost:9042.
[cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.
cqlsh> CAPTURE 'abc.log'
Now capturing query output to 'abc.log'.
cqlsh> SELECT cluster_name from system.local ;
cqlsh> SELECT listen_address from system.local ;
cqlsh> show VERSION
[cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4]
cqlsh> CAPTURE off;
cqlsh> CAPTURE
Currently not capturing query output.
cqlsh> CAPTURE ;
Currently not capturing query output.
cqlsh> quit
[root@much ~]# cat abc.log
cluster_name
--------------
Test Cluster
(1 rows)
listen_address
----------------
127.0.0.1
(1 rows)
[root@much ~]#Begins capturing command output and appending it to a specified file. Output will not be shown at the console while it is captured. Only query result output is captured. Errors and output from cqlsh-only commands will still be shown in the cqlsh session o inspect the current capture configuration, use CAPTURE with no arguments.
HELP
帮助命令
不加参数显现所有的命令
加上命令就对指定的命令进行解释
代码语言：javascript复制cqlsh> HELP
Documented shell commands:
===========================
CAPTURE CLS COPY DESCRIBE EXPAND LOGIN SERIAL SOURCE UNICODE
CLEAR CONSISTENCY DESC EXIT HELP PAGING SHOW TRACING
CQL help topics:
================
AGGREGATES CREATE_KEYSPACE DROP_TRIGGER TEXT
ALTER_KEYSPACE CREATE_MATERIALIZED_VIEW DROP_TYPE TIME
ALTER_MATERIALIZED_VIEW CREATE_ROLE DROP_USER TIMESTAMP
ALTER_TABLE CREATE_TABLE FUNCTIONS TRUNCATE
ALTER_TYPE CREATE_TRIGGER GRANT TYPES
ALTER_USER CREATE_TYPE INSERT UPDATE
APPLY CREATE_USER INSERT_JSON USE
ASCII DATE INT UUID
BATCH DELETE JSON
BEGIN DROP_AGGREGATE KEYWORDS
BLOB DROP_COLUMNFAMILY LIST_PERMISSIONS
BOOLEAN DROP_FUNCTION LIST_ROLES
COUNTER DROP_INDEX LIST_USERS
CREATE_AGGREGATE DROP_KEYSPACE PERMISSIONS
CREATE_COLUMNFAMILY DROP_MATERIALIZED_VIEW REVOKE
CREATE_FUNCTION DROP_ROLE SELECT
CREATE_INDEX DROP_TABLE SELECT_JSON
cqlsh> HELP HELP
HELP [cqlsh only]
Gives information about cqlsh commands. To see available topics,
enter "HELP" without any arguments. To see help on a topic,
use "HELP <topic>".
cqlsh> HELP SELECT_JSON
*** No browser to display CQL help. URL for help topic SELECT_JSON : https://cassandra.apache.org/doc/cql3/CQL-3.2.html#selectJson
cqlsh> HELP SELECT
*** No browser to display CQL help. URL for help topic SELECT : https://cassandra.apache.org/doc/cql3/CQL-3.2.html#selectStmt
cqlsh> HELP CAPTURE
CAPTURE [cqlsh only]
Begins capturing command output and appending it to a specified file.
Output will not be shown at the console while it is captured.
Usage:
CAPTURE '<file>';
CAPTURE OFF;
CAPTURE;
That is, the path to the file to be appended to must be given inside a
string literal. The path is interpreted relative to the current working
directory. The tilde shorthand notation ('~/mydir') is supported for
referring to $HOME.
Only query result output is captured. Errors and output from cqlsh-only
commands will still be shown in the cqlsh session.
To stop capturing output and show it in the cqlsh session again, use
CAPTURE OFF.
To inspect the current capture configuration, use CAPTURE with no
arguments.
cqlsh> HELP APPLY
*** No browser to display CQL help. URL for help topic APPLY : https://cassandra.apache.org/doc/cql3/CQL-3.2.html#batchStmt
cqlsh> HELP EXIT
EXIT/QUIT [cqlsh only]
Exits cqlsh.
cqlsh>总结
CQL 的这些命令还是比较简单好用的，但目前为止还没涉及到操作数据
