限制使用 Redis 实现数量限制（redis数量）

Redis is a widely used open source, in-memory data structure store that is often used for caching application data and for implementing various high-performance features. For example, one of the key features that makes Redis so attractive is its ability to limit the number of requests that can be processed in a given time frame, or to limit the number of objects that can be stored in a given data store.

In this article, we’ll discuss how you can use Redis to limit the number of requests or objects stored in a data store over a given period of time. We’ll explore how to achieve this through the use of keys, hashes and sets.

First, let’s assume we want to limit the number of requests that can be made in a given hour. We can achieve this by creating a key in Redis with the following properties:

key name: ratelimit_requests_per_hour

value: 3600 (3600 seconds in an hour)

Using this key, we can then create a hash to store the counts for each hour. Each element in the hash would then contain the timestamp of when the request was made, and the count associated with that request. To ensure accuracy, we should use a multi-key operations (MGET/MSET) to prevent race conditions.

To update the hash for each request, we need to use a MULTI command along with the appropriate set and incr operations to add a count for the given request. Here is an example in Lua:

local curremt_ts = redis.call(‘time’)[1]

if redis.call(‘hexists’, ‘ratelimit_requests_per_hour’, curremt_ts) == 0 then

redis.call(‘hset’, ‘ratelimit_requests_per_hour’, curremt_ts, 1)

else

redis.call(‘hincrby’, ‘ratelimit_requests_per_hour’, curremt_ts, 1)

end

Finally, to determine whether the request should be blocked, we can set a threshold and add a set to our Redis data store that keeps track of all the timestamps that exceed the threshold. Here is an example of the set and a ZREVRANGE operation that we can use to retrieve the timestamps for the top 10 requests for the given hour:

// add the current timestamp to the set

redis.call(‘zadd’, ‘ratelimit_requests_set’, curremt_ts, 1)

// retrieve the highest 10 requests for the hour

local top10 = redis.call(‘zrevrange’, ‘ratelimit_requests_set’, 0, 10)

If the current timestamp is included in the set, then we can reject the request for exceeding the limit and take appropriate measures.

In this article, we’ve discussed how you can use Redis to limit the number of requests or objects stored in a data store over a given period of time. We discussed how to achieve this through the use of keys, hashes and sets. Through the combination of these data structures, Redis makes it easy to limit the number of requests or objects that can be stored.