Redis GET 与 SQL SELECT [英] Redis GET vs. SQL SELECT

问题描述

我对 NoSQL 很陌生，但我一直很喜欢它的想法.我查看了 Redis，并得到了一些关于存储和接收多个 哈希的最佳方法的问题.

I am pretty new to NoSQL, but I always liked the idea of it. I took a look at Redis, and got a few questions about the best ways of storing and recieving multiple hashes.

假设以下场景:

Store a list of objects (redis 'Hashes') and select them by their timestamp.

要在 SQL 中存档，需要一张表和两个简单​​的查询(INSERT & SELECT).

To archive this in SQL, it would require one table and two simple queries (INSERT & SELECT).

尝试在 Redis 中执行此操作，我最终创建了以下结构:

Trying to do this in Redis, I ended up creating the following structure:

1. Key object:$id (hash) 包含 object
2. Key index:timestamp:$id (排序集)score 等于 timestamp 和 value 包括 id

1. Key object:$id (hash) containing the object
2. Key index:timestamp:$id (sorted set) score equals timestamp and value includes id

虽然我可以忍受两个键而不是一个表的额外维护工作 (SQL)，但我对选择多个对象的过程感到好奇:

While I can live with the additional maintenance work of two keys instead of one table (SQL), I am curious about the process of selecting multiple objects:

ZRANGEBYSCORE index:timestamp:$id timestampStart timestampEnd

这将返回在 timestampStart 和 timestampEnd 之间创建的所有 ID 的 array.为了获取对象本身，我通过以下方式请求每个对象:

This returns an array of all IDs which got created between timestampStart and timestampEnd. To get the object itself I am requesting every single one by:

GET object:$id 

• 这是正确的做法吗?
• 与 SQL 数据库相比:它是否仍然明显更快，或者由于 GET 的数量过多，它甚至可能变得更慢?
• Is this the right way of doing it?
• In comparison with an SQL Database: Is it still appreciably faster or might it even become slower caused by the high number of GETs?

推荐答案

A ZRANGEBYSCORE 成本 O(log(N) + M) where N=|您的集合中的项目| 和 M=|您选择的项目|.因此，执行 ZRANGEBYSCORE 然后 M GET 操作只是 O(long(N)+M+M) = O(log(N)+M) 并且最多会慢两倍.网络来回可能会严重减慢，但由于您的每个 get 都是独立的操作，因此您可以将它们流水线化.您也可以将整个内容放在 Lua 脚本中，然后来回进行一次，这将是最佳的.我可以 99% 肯定地说，这比在 SQL 中做同样的事情要快.

A ZRANGEBYSCORE costs O(log(N) + M) where N=|items in your set| and M=|items you're selecting|. So, doing the ZRANGEBYSCORE and then M GET operations is just O(long(N)+M+M) = O(log(N)+M) and would at most be twice as slow. The network back and forth could have been a major slow down, but since each of your gets is an independent operation, you can just pipeline them. You can also put the whole thing in a Lua script and just have one back and forth, which would be the most optimal. I'd say with 99% certainty this would be faster than doing the same thing in SQL.

此外，如果这对您来说是一个非常频繁的操作，您可以通过将整个对象存储在排序集中而不是仅存储 id 来提高速度.您将 key = object 编码为 json，score = timestamp.就不需要执行任何 GET 操作而言，这将为您的操作节省 <​​code>O(M).

Also, if this is a very frequent operation for you, you can get even more speed up by just storing the entire object in your sorted set instead of just the id. You'd have key = object encoded as json, score = timestamp. This would save you O(M) on your operation in terms of not needing to do any GETs.

这是否是一种好的做事方式实际上取决于您的用例.您真正需要多少速度，传统数据库的其他功能对您来说有多重要?请记住，与传统数据库相比，Redis 不仅仅是客户端可访问的数据结构，它必须将所有内容存储在 RAM 中.要了解这是否适合您，我们需要更多信息.

Whether or not this is a good way of doing things really depends on your use case. How much speed do you really need, and how important are other features of a traditional database to you? Remember, Redis is much more just datastructures accessible by clients than a traditional database, and it must store everything in RAM. To know whether it's the right thing for you, we'd need more information.

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