所以，我来到了一个地方，我想把我存储在redis的数据分割成单独的数据库，因为我有时需要在一种特定的数据上使用键命令，并想把它分开，以使其更快。
If I segment into multiple databases, everything is still single threaded, and I still only get to use one core. If I just launch another instance of Redis on the same box, I get to use an extra core. On top of that, I can't name Redis databases, or give them any sort of more logical identifier. So, with all of that said, why/when would I ever want to use multiple Redis databases instead of just spinning up an extra instance of Redis for each extra database I want? And relatedly, why doesn't Redis try to utilize an extra core for each extra database I add? What's the advantage of being single threaded across databases?
你不希望在一个redis实例中使用多个数据库。正如您所指出的，多个实例使您可以利用多个内核。如果使用数据库选择，则升级时必须进行重构。监视和管理多个实例并不困难，也不痛苦。
实际上，通过基于实例的隔离，您可以获得对每个db更好的度量。每个实例都有反映该数据段的统计信息，这可以实现更好的调优、响应更及时、更准确的监控。使用最新版本并按实例分隔数据。
正如Jonaton所说，不要使用按键命令。如果您只是创建一个键索引，您将发现更好的性能。无论何时添加键，都要将键名添加到集合中。keys命令在扩展后并不是特别有用，因为返回它将花费大量时间。
让访问模式决定如何构建数据，而不是按照您认为有效的方式存储数据，然后再考虑如何访问和切碎数据。您将看到更好的性能，并发现数据消费代码通常更干净和更简单。
对于单线程，考虑redis是为速度和原子性而设计的。当然，在一个db中修改数据的操作不需要等待另一个db，但是如果该操作保存到转储文件中，或者在slave上处理事务呢?在这一点上，您开始进入并发编程的杂草。
通过使用多个实例，您可以将多线程的复杂性转化为更简单的消息传递样式系统。
原则上，相同实例上的Redis数据库与RDBMS数据库实例中的模式没有区别。
所以，说了这么多，为什么/什么时候我想要使用倍数
Redis数据库，而不是仅仅旋转一个额外的Redis实例
为我想要的每个额外数据库?
There's one clear advantage of using redis databases in the same redis instance, and that's management. If you spin up a separate instance for each application, and let's say you've got 3 apps, that's 3 separate redis instances, each of which will likely need a slave for HA in production, so that's 6 total instances. From a management standpoint, this gets messy real quick because you need to monitor all of them, do upgrades/patches, etc. If you don't plan on overloading redis with high I/O, a single instance with a slave is simpler and easier to manage provided it meets your SLA.
甚至Salvatore Sanfilippo (Redis的创造者)也认为在Redis中使用多个db是一个坏主意。点击这里查看他的评论:
https://groups.google.com/d/topic/redis-db/vS5wX8X4Cjg/discussion
I understand how this can be useful, but unfortunately I consider
Redis multiple database errors my worst decision in Redis design at
all... without any kind of real gain, it makes the internals a lot
more complex. The reality is that databases don't scale well for a
number of reason, like active expire of keys and VM. If the DB
selection can be performed with a string I can see this feature being
used as a scalable O(1) dictionary layer, that instead it is not.
With DB numbers, with a default of a few DBs, we are communication
better what this feature is and how can be used I think. I hope that
at some point we can drop the multiple DBs support at all, but I think
it is probably too late as there is a number of people relying on this
feature for their work.
