The Good, the Bad, and the Ugly Among Redis Pagination Strategies

If you need to use pagination in your Redis app, there are a couple of strategies you can use to achieve the necessary functionality. While pagination can be challenging, a quick overview of each of these techniques should be helpful in making your job of choosing a method and implementing it a little easier. There are several strategies for pagination in Redis. Find out what they are and the pros and cons of each!

In Redis, you have a couple of options from which to choose. You can use the SSCAN command or you can use sorted sets. Each of these has their own advantages, so choose the one that works best for your application and its infrastructure.

Using the SSCAN Command

The SSCAN command is part of a group of commands similar to the regular SCAN command. These include:

• SCAN - Used to iterate over the set of keys in the current database.
• SSCAN - Used to iterate over elements of sets.
• HSCAN - Used to iterate fields hashes and associated values.
• ZSCAN - Used to iterate elements of sorted sets and their scores.

Example of scan iteration. Source: Redis.

So, while the regular SCAN command iterates over the database keys, the SSCAN command can iterate over elements of sets. By using the returned SSCAN cursor, you could paginate over a Redis set.

The downside is that you need some way to persist the value of the cursor, and if there are concurrent users this could lead to some odd behavior, since the cursor may not be where it is expected. However, this can be useful for applications where traffic to these paginated areas may be lighter.

Using Sorted Sets

In Redis, sorted sets are a non-repeating collection of strings associated with a score. This score is used to order the set from the smallest to the largest score. This data type allows for fast updating by giving you easy access to elements, even if the elements are in the middle of the set.

An example of sorted set elements Source: Redis.

To paginate, you can use the ZRANGE command to select a range of elements in a sorted set based on their scores. So, you could, for example, select scores from 1-20, 21-40, and so on. By programmatically adjusting the range as the user moves through the data, you can achieve the pagination you need for your application.

Since sorted sets and ZRANGE do this task more intuitively than using a scan, it is often the preferred method of pagination, and is easier to implement with multiple users, since you can programmatically keep track of which ZRANGE each user is selecting at any given time.

In the end, you can choose which method works for your particular situation. If you have a smaller application with less traffic, a scan may work for you. If, however, you need a more robust solution for larger data sets or more highly utilized applications, it may be best to go ahead and use ZRANGE with sorted sets to achieve pagination in your application.