cassandra README

The project's README from github.com/apache/cassandra. As one markdown file: README.md.

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Apache Cassandra

Apache Cassandra is a highly-scalable partitioned row store. Rows are organized into tables with a required primary key.

https://cwiki.apache.org/confluence/display/CASSANDRA2/Partitioners[Partitioning] means that Cassandra can distribute your data across multiple machines in an application-transparent matter. Cassandra will automatically repartition as machines are added and removed from the cluster.

https://cwiki.apache.org/confluence/display/CASSANDRA2/DataModel[Row store] means that like relational databases, Cassandra organizes data by rows and columns. The Cassandra Query Language (CQL) is a close relative of SQL.

For more information, see https://cassandra.apache.org/[the Apache Cassandra web site].

Issues should be reported on https://issues.apache.org/jira/projects/CASSANDRA/issues/[The Cassandra Jira].

Requirements

Getting started

This short guide will walk you through getting a basic one node cluster up and running, and demonstrate some simple reads and writes. For a more-complete guide, please see the Apache Cassandra website's https://cassandra.apache.org/doc/latest/cassandra/getting-started/index.html[Getting Started Guide].

First, we'll unpack our archive:

$ tar -zxvf apache-cassandra-$VERSION.tar.gz $ cd apache-cassandra-$VERSION

After that we start the server. Running the startup script with the -f argument will cause Cassandra to remain in the foreground and log to standard out; it can be stopped with ctrl-C.

$ bin/cassandra -f

Now let's try to read and write some data using the Cassandra Query Language:

$ bin/cqlsh

The command line client is interactive so if everything worked you should be sitting in front of a prompt:

Connected to Test Cluster at localhost:9160. [cqlsh 6.3.0 | Cassandra 7.0-SNAPSHOT | CQL spec 3.4.8 | Native protocol v5] Use HELP for help. cqlsh>

As the banner says, you can use 'help;' or '?' to see what CQL has to offer, and 'quit;' or 'exit;' when you've had enough fun. But lets try something slightly more interesting:

cqlsh> CREATE KEYSPACE schema1 WITH replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 }; cqlsh> USE schema1; cqlsh:Schema1> CREATE TABLE users ( user_id varchar PRIMARY KEY, first varchar, last varchar, age int ); cqlsh:Schema1> INSERT INTO users (user_id, first, last, age) VALUES ('jsmith', 'John', 'Smith', 42); cqlsh:Schema1> SELECT * FROM users; user_id | age | first | last ---------+-----+-------+------- jsmith | 42 | john | smith

cqlsh:Schema1>

If your session looks similar to what's above, congrats, your single node cluster is operational!

For more on what commands are supported by CQL, see https://cassandra.apache.org/doc/trunk/cassandra/developing/cql/index.html[the CQL reference]. A reasonable way to think of it is as, "SQL minus joins and subqueries, plus collections."

Wondering where to go from here?

cassandra (apache/cassandra)

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10.1K ·GitHub
Cassandra
这是什么?Apache Cassandra 是一个开源的事务型分布式数据库——一种高可扩展性的分区行存储,专为在普通硬件或云基础设施上实现线性扩展和经过验证的容错能力而设计。
这是我要运行的服务器,还是嵌入到我应用里的库?它是一个数据库服务器,而不是库:你要把它作为一组节点的集群来运行,然后通过网络用 CQL(Cassandra Query Language)来查询,比如使用自带的交互式客户端 cqlsh。
怎么搭建一个最基本的双……不对,单节点集群并跑起来?解压发布包(tar -zxvf apache-cassandra-$VERSION.tar.gz),用 'bin/cassandra -f' 启动服务器(它会保持在前台运行并把日志输出到标准输出;按 Ctrl-C 即可停止),然后运行 'bin/cqlsh' 来创建表和读写数据。
启动之前需要先装好什么?需要一个受支持的 Java 版本——具体列表见 build.xml 中的 java.supported 属性——此外还需要 Python,cqlsh 命令行工具依赖它(其支持的版本会在 bin/cqlsh 中检查)。
CQL 和 SQL 有多接近——我能直接写平时习惯的 SQL 吗?CQL 和 SQL 非常接近,但可以把它理解为'SQL 去掉连接和子查询,再加上集合类型'。如果你的业务负载大量依赖连接或子查询,就得围绕这一点重新设计表结构。
往集群里加机器或删机器时,我的数据会怎么样?Cassandra 会自动重新平衡:当机器增加或减少时,它会自动重新划分数据分区,并把数据透明地分布到各个节点上,应用完全感知不到。
第一次用 CQL 实际操作是什么样子?在 cqlsh 里先创建一个带副本设置(例如副本因子为 1 的 SimpleStrategy)的 keyspace,然后用 userid 作为 PRIMARY KEY 执行 CREATE TABLE users,INSERT 一行数据再 SELECT 回来——这时你的单节点集群就已经可用了。
内部的数据模型是怎么组织的?和关系型数据库类似:行组织在表中,并且必须有主键。区别在于这个存储是分区的,所以行分散在集群的多台机器上,而不是集中放在一台服务器里。
What are similar projects?scylladb, nebula, tidb, zookeeper, druid, foundationdb, yugabyte-db, trino
Which topics is it in?cassandra, apache, distributed-database, scalability, big-data, nosql, storage, sql, distributed-systems, cloud, java, backend
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