为什么要使用非关系数据库？ [英] Why would I want to use a non-relational database?

问题描述

数据库中最新的热潮似乎围绕着非关系数据库。为什么？这似乎是适得其反。例如，我以一种关系方式（表格的Django + SQL中的示例代码）表达我的数据更有意义：

  class Post（models.Model）：
 name = models.CharField（）
 created = models.DateTimeField（auto_now_create = True）
 
类注释）：
 text = models.TextField（）
 post = models.ForeignKey（'Post'）
 created = models.DateTimeField（auto_now_create = True）
  

SQL：

  id int primary key auto_increment，
 name varchar，
 created datetime）; 
 
 create table comment（id int primary key auto_increment，
 text text，
 post_id int，
 created datetime，
 foreign key post_id references post ））; 
  

SQL的优点是这些信息可以用方法。当然，整个对象 - 关系映射问题存在，但我把它看作一个特性，而不是一个问题。使用SQL，我可以获取早于昨天的所有不同的评论，整理所有这些，并生成统计信息。对于非关系数据库也可以这样做？

使用MongoDB这样的非关系数据库似乎真的会影响性能，因为你会立即抓取整个对象图，而不是你最少需要的。

有人可以向我解释使用非关系数据库的好处吗？

解决方案

查看 CAP定理

并且 PACELC解释

关系数据库倾向于做出一组权衡，和非关系倾向于做出一组不同的权衡。对于大规模分布式数据集，非关系有时更有意义。

还有一种感觉，其中非关系数据库可以消除很多ORM痛苦，总是有权衡。在某些使用情况下，非关系存储可以更快，因为特定层次结构的所有数据可以更紧密地存储在磁盘上。还要注意，非关系数据库仍然具有查询功能。

最后，它是为您的特定用例做出适当的权衡集。 / p>

The latest craze in databases seems to be centered around non-relational databases. Why? It seems kind of counterproductive. For example, it makes much more sense to me to express my data in a relational way (example code in Django + SQL for tables):

class Post(models.Model):
    name = models.CharField()
    created = models.DateTimeField(auto_now_create = True)

class Comment(models.Model):
    text = models.TextField()
    post = models.ForeignKey('Post')
    created = models.DateTimeField(auto_now_create = True)

SQL:

create table post (id int primary key auto_increment,
        name varchar,
        created datetime);

create table comment(id int primary key auto_increment,
        text text,
        post_id int,
        created datetime,
        foreign key post_id references post(id));

The power of SQL is that this information can be expressed in so many ways. Sure, the whole object-relational-mapping problem exists, but I look at it as a feature and not as a problem. With SQL, I can fetch all distinct comments of a given post which are older than yesterday, collate all of those together, and generate statistics. Can the same be done for non-relational databases?

It also would seem to really impact performance to use a non-relational database like MongoDB because you would immediately grab an entire object graph, rather than what you minimally need.

Can someone explain to me what the benefits are of using a non-relational database?

解决方案

Take a look at the CAP Theorem

And the PACELC interpretation

Relational databases tend to make one set of trade-offs, and non-relational tend to make a different set of trade-offs. For massive distributed datasets, non-relational sometimes makes more sense.

There is also a sense in which non-relational databases can eliminate a lot of the ORM pain, but again there are always tradeoffs. In some use cases, non-relational storage can be faster, because all the data for a particular hierarchy can be stored closer together on the disk. Also note that non-relational databases do still have query capabilities.

In the end, it's about making the appropriate set of trade-offs for your particular use-case.

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