在这里，我将重点介绍一些重要的方面，这些方面可以帮助你决定是否真的需要卡桑德拉。这个清单并不详尽，只是我脑海中最重要的一些观点

Don't consider Cassandra as the first choice when you have a strict requirement on the relationship (across your dataset). Cassandra by default is AP system (of CAP). But, it supports tunable consistency which means it can be configured to support as CP as well. So don't ignore it just because you read somewhere that it's AP and you are looking for CP systems. Cassandra is more accurately termed “tuneably consistent,” which means it allows you to easily decide the level of consistency you require, in balance with the level of availability. Don't use Cassandra if your scale is not much or if you can deal with a non-distributed DB. Think harder if your team thinks that all your problems will be solved if you use distributed DBs like Cassandra. To start with these DBs is very simple as it comes with many defaults but optimizing and mastering it for solving a specific problem would require a good (if not a lot) amount of engineering effort. Cassandra is column-oriented but at the same time each row also has a unique key. So, it might be helpful to think of it as an indexed, row-oriented store. You can even use it as a document store. Cassandra doesn't force you to define the fields beforehand. So, if you are in a startup mode or your features are evolving (as in agile) - Cassandra embraces it. So better, first think about queries and then think about data to answer them. Cassandra is optimized for really high throughput on writes. If your use case is read-heavy (like cache) then Cassandra might not be an ideal choice.

Cassandra是一个特定问题的答案:当您有太多数据，以至于无法在一台服务器上存储时，您该怎么办?如何将所有数据存储在多个服务器上，同时不破坏银行账户，不让开发人员抓狂?Facebook每天都会收到4tb的压缩数据。这个数字很可能在一年内增长两倍以上。

如果您没有这么多数据，或者您有数百万美元来支付企业Oracle/DB2集群安装费用，以及安装和维护它所需的专家，那么您可以使用SQL数据库。

然而，Facebook不再使用cassandra，现在几乎只使用MySQL，在应用程序堆栈中移动分区，以获得更快的性能和更好的控制。

在评估分布式数据系统时，您必须考虑CAP定理——您可以选择以下两个:一致性、可用性和分区容差。

Cassandra是一个可用的、支持最终一致性的分区容忍系统。要了解更多信息，请参阅我写的这篇博客文章:NoSQL系统的可视化指南。

让我们来读一些真实的案例:

http://planetcassandra.org/apache-cassandra-use-cases/

本文地址:http://planetcassandra.org/blog/post/agentis-energy-stores-over-15-billion-records-of-time-series-usage-data-in-apache-cassandra

他们详细阐述了不选择MySql的原因，因为数据库同步太慢。

(也是由于2- phase commit, FK, PK)

Cassandra基于Amazon Dynamo纸

特点:

稳定

高可用性

备份性能良好

读写比HBase好，(java中的BigTable克隆)。

wiki http://en.wikipedia.org/wiki/Apache_Cassandra

他们的结论是:

We looked at HBase, Dynamo, Mongo and Cassandra. 

Cassandra was simply the best storage solution for the majority of our data.

截至2018年，

如果你需要支援，我建议你用ScyllaDB代替经典的cassandra。

Postgres kv插件也比cassandra快。无论如何不会有多实例可伸缩性。

在部署Cassandra的过程中与某人交谈，它不能很好地处理多对多。他们正在做初步测试。我和Cassandra的顾问谈过这个问题，他说如果你有这样的习题集，他就不建议你这么做。

Cassandra是个不错的选择，如果:

您不需要DB中的ACID属性。 DB上会有大量的写操作。 需要与大数据、Hadoop、Hive和Spark集成。 需要实时数据分析和生成报告。 有一个强大的容错机制的要求。 有一个齐次系统的要求。 调优需要大量的自定义。