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
接着上一篇，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
TRACING
用于跟踪一条语句的执行过程
代码语言：javascript复制Enables or disables tracing for queries. When tracing is enabled, once a query completes, a trace of the events during the query will be printed.
cqlsh> TRACING on
Now Tracing is enabled
cqlsh> SELECT listen_address from system.local ;
listen_address
----------------
127.0.0.1
(1 rows)
Tracing session: 254857b0-0299-11e8-9160-dd31d8caf67e
activity | timestamp | source | source_elapsed | client
-------------------------------------------------------------------------------------------------------------------------------- ---------------------------- ----------- ---------------- -----------
Execute CQL3 query | 2018-01-26 21:02:21.356000 | 127.0.0.1 | 0 | 127.0.0.1
Parsing SELECT listen_address from system.local ; [Native-Transport-Requests-1] | 2018-01-26 21:02:21.360000 | 127.0.0.1 | 3809 | 127.0.0.1
Preparing statement [Native-Transport-Requests-1] | 2018-01-26 21:02:21.360000 | 127.0.0.1 | 4215 | 127.0.0.1
Computing ranges to query [Native-Transport-Requests-1] | 2018-01-26 21:02:21.360000 | 127.0.0.1 | 4541 | 127.0.0.1
Submitting range requests on 1 ranges with a concurrency of 1 (30.07059 rows per range expected) [Native-Transport-Requests-1] | 2018-01-26 21:02:21.361000 | 127.0.0.1 | 4779 | 127.0.0.1
Submitted 1 concurrent range requests [Native-Transport-Requests-1] | 2018-01-26 21:02:21.361000 | 127.0.0.1 | 4935 | 127.0.0.1
Executing seq scan across 2 sstables for (min(-9223372036854775808), min(-9223372036854775808)) [ReadStage-2] | 2018-01-26 21:02:21.363000 | 127.0.0.1 | 7084 | 127.0.0.1
Read 1 live and 0 tombstone cells [ReadStage-2] | 2018-01-26 21:02:21.364000 | 127.0.0.1 | 8537 | 127.0.0.1
Request complete | 2018-01-26 21:02:21.366302 | 127.0.0.1 | 10302 | 127.0.0.1
cqlsh> TRACING off
Disabled Tracing.
cqlsh> SELECT listen_address from system.local ;
listen_address
----------------
127.0.0.1
(1 rows)
cqlsh>PAGING
用来配置会话里的页显条数
不加参数时打开默认为每页 100 条，也可以在打开时直接指定一页的条目数
代码语言：javascript复制Enables paging, disables paging, or sets the page size for read queries. When paging is enabled, only one page of data will be fetched at a time and a prompt will appear to fetch the next page. Generally, it’s a good idea to leave paging enabled in an interactive session to avoid fetching and printing large amounts of data at once.
cqlsh> PAGING on
Now Query paging is enabled
Page size: 100
cqlsh> PAGING off
Disabled Query paging.
cqlsh> PAGING 5
Page size: 5
cqlsh> select * from system_schema.columns ;
keyspace_name | table_name | column_name | clustering_order | column_name_bytes | kind | position | type
--------------- -------------------------------- ------------- ------------------ -------------------------- --------------- ---------- -----------
system_auth | resource_role_permissons_index | resource | none | 0x7265736f75726365 | partition_key | 0 | text
system_auth | resource_role_permissons_index | role | asc | 0x726f6c65 | clustering | 0 | text
system_auth | role_members | member | asc | 0x6d656d626572 | clustering | 0 | text
system_auth | role_members | role | none | 0x726f6c65 | partition_key | 0 | text
system_auth | role_permissions | permissions | none | 0x7065726d697373696f6e73 | regular | -1 | set<text>
---MORE---
keyspace_name | table_name | column_name | clustering_order | column_name_bytes | kind | position | type
--------------- ------------------ -------------- ------------------ ---------------------------- --------------- ---------- -----------
system_auth | role_permissions | resource | asc | 0x7265736f75726365 | clustering | 0 | text
system_auth | role_permissions | role | none | 0x726f6c65 | partition_key | 0 | text
system_auth | roles | can_login | none | 0x63616e5f6c6f67696e | regular | -1 | boolean
system_auth | roles | is_superuser | none | 0x69735f737570657275736572 | regular | -1 | boolean
system_auth | roles | member_of | none | 0x6d656d6265725f6f66 | regular | -1 | set<text>
---MORE---
keyspace_name | table_name | column_name | clustering_order | column_name_bytes | kind | position | type
--------------- ------------ ---------------- ------------------ -------------------------------- --------------- ---------- --------------------
system_auth | roles | role | none | 0x726f6c65 | partition_key | 0 | text
system_auth | roles | salted_hash | none | 0x73616c7465645f68617368 | regular | -1 | text
system_schema | aggregates | aggregate_name | asc | 0x6167677265676174655f6e616d65 | clustering | 0 | text
system_schema | aggregates | argument_types | asc | 0x617267756d656e745f7479706573 | clustering | 1 | frozen<list<text>>
system_schema | aggregates | final_func | none | 0x66696e616c5f66756e63 | regular | -1 | text
---MORE---
cqlsh>EXPAND
将默认为行显转换为列显
在行显而列数太多的时候，使用这种方式，展示会更友好
代码语言：javascript复制Enables or disables vertical printing of rows. Enabling EXPAND is useful when many columns are fetched, or the contents of a single column are large.
cqlsh> EXPAND
Expanded output is currently disabled. Use EXPAND ON to enable.
cqlsh> EXPAND on
Now Expanded output is enabled
cqlsh> select * from system_schema.columns limit 1;
@ Row 1
------------------- --------------------------------
keyspace_name | system_auth
table_name | resource_role_permissons_index
column_name | resource
clustering_order | none
column_name_bytes | 0x7265736f75726365
kind | partition_key
position | 0
type | text
(1 rows)
cqlsh> select * from system_schema.columns limit 2;
@ Row 1
------------------- --------------------------------
keyspace_name | system_auth
table_name | resource_role_permissons_index
column_name | resource
clustering_order | none
column_name_bytes | 0x7265736f75726365
kind | partition_key
position | 0
type | text
@ Row 2
------------------- --------------------------------
keyspace_name | system_auth
table_name | resource_role_permissons_index
column_name | role
clustering_order | asc
column_name_bytes | 0x726f6c65
kind | clustering
position | 0
type | text
(2 rows)
cqlsh> EXPAND off
Disabled Expanded output.
cqlsh> select * from system_schema.columns limit 1;
keyspace_name | table_name | column_name | clustering_order | column_name_bytes | kind | position | type
--------------- -------------------------------- ------------- ------------------ -------------------- --------------- ---------- ------
system_auth | resource_role_permissons_index | resource | none | 0x7265736f75726365 | partition_key | 0 | text
(1 rows)
cqlsh>CLEAR
用来清屏
代码语言：javascript复制cqlsh> help clear
CLEAR/CLS [cqlsh only]
Clears the console.
cqlsh> help cls
CLEAR/CLS [cqlsh only]
Clears the console.
cqlsh> cls
cqlsh>DESCRIBE
显示指定对象的描述信息
代码语言：javascript复制Prints a description (typically a series of DDL statements) of a schema element or the cluster. This is useful for dumping all or portions of the schema.
cqlsh> help describe
DESCRIBE [cqlsh only]
(DESC may be used as a shorthand.)
Outputs information about the connected Cassandra cluster, or about
the data objects stored in the cluster. Use in one of the following ways:
DESCRIBE KEYSPACES
Output the names of all keyspaces.
DESCRIBE KEYSPACE [<keyspacename>]
Output CQL commands that could be used to recreate the given keyspace,
and the objects in it (such as tables, types, functions, etc.).
In some cases, as the CQL interface matures, there will be some metadata
about a keyspace that is not representable with CQL. That metadata will not be shown.
The '<keyspacename>' argument may be omitted, in which case the current
keyspace will be described.
DESCRIBE TABLES
Output the names of all tables in the current keyspace, or in all
keyspaces if there is no current keyspace.
DESCRIBE TABLE [<keyspace>.]<tablename>
Output CQL commands that could be used to recreate the given table.
In some cases, as above, there may be table metadata which is not
representable and which will not be shown.
DESCRIBE INDEX <indexname>
Output the CQL command that could be used to recreate the given index.
In some cases, there may be index metadata which is not representable
and which will not be shown.
DESCRIBE MATERIALIZED VIEW <viewname>
Output the CQL command that could be used to recreate the given materialized view.
In some cases, there may be materialized view metadata which is not representable
and which will not be shown.
DESCRIBE CLUSTER
Output information about the connected Cassandra cluster, such as the
cluster name, and the partitioner and snitch in use. When you are
connected to a non-system keyspace, also shows endpoint-range
ownership information for the Cassandra ring.
DESCRIBE [FULL] SCHEMA
Output CQL commands that could be used to recreate the entire (non-system) schema.
Works as though "DESCRIBE KEYSPACE k" was invoked for each non-system keyspace
k. Use DESCRIBE FULL SCHEMA to include the system keyspaces.
DESCRIBE TYPES
Output the names of all user-defined-types in the current keyspace, or in all
keyspaces if there is no current keyspace.
DESCRIBE TYPE [<keyspace>.]<type>
Output the CQL command that could be used to recreate the given user-defined-type.
DESCRIBE FUNCTIONS
Output the names of all user-defined-functions in the current keyspace, or in all
keyspaces if there is no current keyspace.
DESCRIBE FUNCTION [<keyspace>.]<function>
Output the CQL command that could be used to recreate the given user-defined-function.
DESCRIBE AGGREGATES
Output the names of all user-defined-aggregates in the current keyspace, or in all
keyspaces if there is no current keyspace.
DESCRIBE AGGREGATE [<keyspace>.]<aggregate>
Output the CQL command that could be used to recreate the given user-defined-aggregate.
DESCRIBE <objname>
Output CQL commands that could be used to recreate the entire object schema,
where object can be either a keyspace or a table or an index or a materialized
view (in this order).
cqlsh> DESCRIBE cluster
Cluster: Test Cluster
Partitioner: Murmur3Partitioner
cqlsh> DESCRIBE schema
cqlsh> DESCRIBE keyspaces
system_traces system_schema system_auth system system_distributed
cqlsh> DESCRIBE tables
Keyspace system_traces
----------------------
events sessions
Keyspace system_schema
----------------------
tables triggers views keyspaces dropped_columns
functions aggregates indexes types columns
Keyspace system_auth
--------------------
resource_role_permissons_index role_permissions role_members roles
Keyspace system
---------------
available_ranges peers batchlog transferred_ranges
batches compaction_history size_estimates hints
prepared_statements sstable_activity built_views
"IndexInfo" peer_events range_xfers
views_builds_in_progress paxos local
Keyspace system_distributed
---------------------------
repair_history view_build_status parent_repair_history
cqlsh>EXIT
退出 cqlsh
代码语言：javascript复制cqlsh> help exit
EXIT/QUIT [cqlsh only]
Exits cqlsh.
cqlsh> exit
[root@much ~]#总结
CQL 的这些命令还是比较简单好用的，目前为止还没涉及到操作数据
