Cassandra安装和初次使用
依赖环境
事实上如果你安装的是OpenJDK，然后启动Cassandra它会报警告，说不推荐使用OpenJDK，而且JDK的版本要1.8。
安装Cassandra
我选择的是下载二进制的文件，然后解压安装：
tar -xvf apache-cassandra-3.6-bin.tar.gz cassandra
哦，我的Linux发行版是CentOS 7 x64
这样你就已经安装好了Cassandra了，真是方便（日常吐槽FreeBSD，想用最新版本的Cassandra以我的水平还达不到啊）。
其他的就是看你需不需要配置环境变量以及日志了，反正我就马马虎虎开车上路了。点这里查看详细配置。
启动Cassandra
cassandra -h
Usage: /usr/local/apache-cassandra-3.10/bin/cassandra [-f] [-h] [-p pidfile] [-H dumpfile] [-E errorfile]
- -f 是前台启动
- -h 帮助信息
- -R 是以root启动
Cassandra不推荐你以root来启动它，如果你非要这么干，可以，你得用-R选项
这里我用的一下方式启动：
/usr/local/apache-cassandra-3.10/bin/cassandra -f -R
日志信息就不传上来了，反正没有报错我就当它成功了。
连接并使用Cassandra
连接Cassandra的客户端为cqlsh，先查看一下这个命令的用法：
/usr/local/apache-cassandra-3.10/bin/cqlsh -h
Usage: cqlsh.py [options] [host [port]]
CQL Shell for Apache Cassandra
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-C, --color Always use color output
--no-color Never use color output
--browser=BROWSER The browser to use to display CQL help, where BROWSER
can be:
- one of the supported browsers in
https://docs.python.org/2/library/webbrowser.html.
- browser path followed by %s, example: /usr/bin
/google-chrome-stable %s
--ssl Use SSL
-u USERNAME, --username=USERNAME
Authenticate as user.
-p PASSWORD, --password=PASSWORD
Authenticate using password.
-k KEYSPACE, --keyspace=KEYSPACE
Authenticate to the given keyspace.
-f FILE, --file=FILE Execute commands from FILE, then exit
--debug Show additional debugging information
--encoding=ENCODING Specify a non-default encoding for output. (Default:
utf-8)
--cqlshrc=CQLSHRC Specify an alternative cqlshrc file location.
--cqlversion=CQLVERSION
Specify a particular CQL version, by default the
highest version supported by the server will be used.
Examples: "3.0.3", "3.1.0"
-e EXECUTE, --execute=EXECUTE
Execute the statement and quit.
--connect-timeout=CONNECT_TIMEOUT
Specify the connection timeout in seconds (default: 5
seconds).
--request-timeout=REQUEST_TIMEOUT
Specify the default request timeout in seconds
(default: 10 seconds).
-t, --tty Force tty mode (command prompt).
Connects to 127.0.0.1:9042 by default. These defaults can be changed by
setting $CQLSH_HOST and/or $CQLSH_PORT. When a host (and optional port number)
are given on the command line, they take precedence over any defaults.
这里我们可以获取一下信息
- cqlsh可以不接任何选项或者参数启动，默认的是连接127.0.0.1:9042端口
其他的选项就不细说了，反正可以直接这样连，赶快连上去看一下。输入cqlsh然后回车。
[root@backup ~]# cqlsh
Connected to Test Cluster at 127.0.0.1:9042.
[cqlsh 5.0.1 | Cassandra 3.10 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.
cqlsh>
嘻嘻，已经连上去了。
输入几个命令体验一把：
查看集群：
cqlsh> desc cluster; // 查看所在的集群
Cluster: Test Cluster
Partitioner: Murmur3Partitioner
查看表空间(姑且先这么称吧)
cqlsh> desc keyspaces; // 查看表空间
system_schema system_auth system myapp system_distributed system_traces
查看具体的表空间
desc keyspace system_schema; // 相当于查看建表语句吧
查看表空间下有哪些表
desc tables;
查看表空间的某张具体表
desc table system_schema.functions;
在使用cql时，如果你不指定表空间，那么你的语句中就必须显示的使用表空间.某张表这样的语句，想要直接使用某张表就要选中表空间了。
使用某个表空间
USE 表空间名; // 是不是跟mysql很像啊
创建表空间
CREATE KEYSPACE myapp WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3};
在这里创建表空间时可以添加某些选项，暂时先这么整，等你你深入之后再研究吧。
使用指定表空间并创建表
cqlsh:system_auth> use myapp;
cqlsh:myapp> CREATE TABLE users (
... id text PRIMARY KEY,
... name text,
... favs map<text, text>
... );
cqlsh:myapp> INSERT INTO users (id, name, favs)
... VALUES ('小明','李小明',{'fruit':'苹果','游戏':'DotA'});
cqlsh:myapp> SELECT * FROM users;
id | favs | name
------+-----------------------------------+--------
小明 | {'fruit': '苹果', '游戏': 'DotA'} | 李小明
(1 rows)
使用where子句查询
cqlsh:myapp> SELECT * FROM user WHERE id="小红";
很不幸，报错了：
'ascii' codec can't encode character u'\u5c0f' in position 72: ordinal not in range(128)
查了一下，这时Python惹得祸。
[root@backup ~]# python
Python 2.7.5 (default, Nov 6 2016, 00:28:07)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-11)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> reload(sys)
<module 'sys' (built-in)>
>>> sys.setdefaultencoding('utf-8')
>>> k=u'中'
>>> print str(unicode(k))
中
>>>
这里我在bin目录下的cqlsh.py文件中添加了如下代码
// 大概就是在这个位置加的
49 from uuid import UUID
50
51 reload(sys) // 这行以及下面的一行
52 sys.setdefaultencoding("utf8")
然后不能用cqlsh这个命令了，只能用cqlsh这个脚本来执行了
[root@backup bin]# ./cqlsh.py
Connected to Test Cluster at 127.0.0.1:9042.
[cqlsh 5.0.1 | Cassandra 3.10 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.
cqlsh> use myapp ;
cqlsh:myapp> select * from user where id="小红";
SyntaxException: line 1:32 no viable alternative at input ';' (...* from user where id=["小]红";)
cqlsh:myapp> select * from user where id="小红"
... ;
SyntaxException: line 2:0 no viable alternative at input ';' (...* from user where id=["小]红";)
cqlsh:myapp> select * from user where id=小红;
Invalid syntax at line 1, char 29
select * from user where id=小红;
^
cqlsh:myapp> select * from user where id='小红';
InvalidRequest: Error from server: code=2200 [Invalid query] message="unconfigured table user"
cqlsh:myapp> select * from user;
InvalidRequest: Error from server: code=2200 [Invalid query] message="unconfigured table user"
cqlsh:myapp> desc myapp
CREATE KEYSPACE myapp WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '3'} AND durable_writes = true;
CREATE TABLE myapp.users (
id text PRIMARY KEY,
favs map<text, text>,
name text
) WITH bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND dclocal_read_repair_chance = 0.1
AND default_time_to_live = 0
AND gc_grace_seconds = 864000
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE';
cqlsh:myapp> select * from users where id='小红';
id | favs | name
------+-----------------------+--------
小红 | {'香水': '香奈儿5号'} | 楚小红
(1 rows)
cqlsh:myapp> select * from user where id="小红" ;
SyntaxException: line 1:33 no viable alternative at input ';' (...* from user where id=["小]红" ;)
cqlsh:myapp> select * from users where id="小红" ;
SyntaxException: line 1:34 no viable alternative at input ';' (...* from users where id=["小]红" ;)
cqlsh:myapp> select * from users where id='小红';
id | favs | name
------+-----------------------+--------
小红 | {'香水': '香奈儿5号'} | 楚小红
(1 rows)
具体执行细节见以上，然后不能用双引号，可以用单引号；我也是......
这里where子句查询的是id，我猜是自带索引的，那就换个列查一下：
cqlsh:myapp> select * from users where name='李小明';
InvalidRequest: Error from server: code=2200 [Invalid query] message="Cannot execute this query as it might involve data filtering and thus may have unpredictable performance. If you want to execute this query despite the performance unpredictability, use ALLOW FILTERING"
cqlsh:myapp> select * from users where name='李小明' allow FILTERING;
id | favs | name
------+-----------------------------------+--------
小明 | {'fruit': '苹果', '游戏': 'DotA'} | 李小明
(1 rows)
网上说要建索引，可我这里也没有建索引啊
建立索引
cqlsh:myapp> create INDEX on users(name);
cqlsh:myapp> select * from users where name='李小明';
id | favs | name
------+-----------------------------------+--------
小明 | {'fruit': '苹果', '游戏': 'DotA'} | 李小明
(1 rows)
好像建立了索引就不会报上面的那条错误，看来是真的要建立索引啊！
P. S.
各位，我搞错了，原来不用修改cqlsh.py的，在where中查询字符串用单引号就可以不用改文件，加字符设置了，不用~~~~
退出Cassandra
找到pid，然后kill之
ps -aux | grep cassandra
马丹，出来好长一串
以上就是初次使用了，很简单的。