I don't really know any benefits of having multiple databases on a single instance. I guess it's useful if multiple services use the same database server(s), so you can avoid key collisions. I would not recommend building around using the KEYS command, since it's O(n) and that doesn't scale well. What are you using it for that you can accomplish in another way? Maybe redis isn't the best match for you if functionality like KEYS is vital. I think they mention the benefits of a single threaded server in their FAQ, but the main thing is simplicity - you don't have to bother with concurrency in any real way. Every action is blocking, so no two things can alter the database at the same time. Ideally you would have one (or more) instances per core of each server, and use a consistent hashing algorithm (or a proxy) to divide the keys among them. Of course, you'll loose some functionality - piping will only work for things on the same server, sorts become harder etc.

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.

在一个实例中使用多个数据库可能在以下场景中有用:

同一数据库的不同副本可以使用实时数据用于生产、开发或测试。人们可以使用replica来克隆一个redis实例来达到同样的目的。然而，前一种方法更容易使现有的正在运行的程序选择正确的数据库切换到预期的模式。

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.

我知道这个问题已经有些年头了，但是多个数据库可能很有用还有另一个原因。

如果你使用你最喜欢的云提供商的“云Redis”，你可能有一个最小的内存大小，并将为你分配的内存付费。然而，如果你的数据集比这个小，那么你就会浪费一些分配，因此也会浪费一些钱。

使用数据库，您可以使用相同的Redis云实例为(比如说)开发、UAT和生产提供服务，或者应用程序的多个实例，或者其他任何东西——这样可以使用更多的已分配内存，因此更划算。

我正在研究的一个用例有几个应用程序实例，每个实例使用20 - 300k，但我的云提供商上的最小分配是1M。我们可以将10个实例合并到一个Redis上，而不受任何限制，因此可以节省大约90%的Redis托管成本。我知道这种方法有局限性和问题，但我认为值得一提。

在极少数情况下，Redis数据库可以用于部署新版本的应用程序，其中新版本需要使用不同的实体。