CODEWITHSUNDEEP
redis
diegoaguilar
diegoaguilar

Reputation: 8376

Is there a way to keep a top N list with Redis?

I work with a MongoDB connection and have a Redis Elastic Cache at hand. There's a Mongo collection which essentially changes a few times per week and it includes a totalPoints for which I'd like to sort some or even all of them, this collection has a huge number of records.

So, sorting demands much work to DB, I really can't pretend to order them at a query, so I'd like to have a TOP list.

I would like to get way to push records, either srtings or objects and order them as a bucket of max size n for the top of those.

Upvotes: 4

Views: 4104

Answers (1)

gladiator
gladiator

Reputation: 742

You can use the pattern described by anitrez here : http://oldblog.antirez.com/post/take-advantage-of-redis-adding-it-to-your-stack.html

Basically just use a sorted set and add the collection values with score as totalPoints.

zadd toplist totalPoints <collectionItemIdentifier>

Then fetch top 100 as 

ZREVRANGE toplist 0 99

You can keep the size in check (it should not be required) by periodically using ZREMRANGEBYSCORE and remove elements whose score is in a certain range.

Check http://redis.io/commands#sorted_set for more information and commands available on sorted set.

Upvotes: 6

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