CODEWITHSUNDEEP
redis
roopunk
roopunk

Reputation: 4361

redis - see if a string contains any key from a set of keys

I have a set of strings, which I was planning to store in a redis set. What I want to do is to check if any of these strings [s] is present inside a subject string ( say S1 ).

I read about SSCAN in redis but it allows me to search if any set member matches a pattern. I want the opposite way round. I want to check if any of the patterns matches my string. Is this possible?

Upvotes: 0

Views: 1746

Answers (2)

Itamar Haber
Itamar Haber

Reputation: 50112

There are several ways to do it, it just depends how you want it done. SSCAN is a perfectly legitimate approach where you do the processing client-side and potentially over the network. Depending on your requirements, this may or may not be a good choice.

The opposite way is to let Redis do it for you, or as much as possible, to save on bandwidth, latency and client cpu. The trade off is, of course, having Redis' cpu do it so it may impact performance in some cases.

When it comes to letting Redis do the work, please first understand that the functionality you're describing is not included in it. So you need to build your own and, again, that depends on your specific use case (e.g. how big are s and S1, is S1 indexable as well, ...). Without this information it is hard to make accurate recommendations but the naive (mine) approach would be to use Lua for the job. The script's logic should either check all permutations of S1 for existence in s with SISMEMBER, or, do Lua pattern matching of all of s's members to S1.

This solution, of course, has plenty of room for optimization if some assumptions/rules are set.

Edit: Sorted sets and ZLEX* stuff are also possibly good for this kind of thing, as @Soveran points out. To augment his example and for further inspiration, see here for a reversed version and think of the possibilities :) I still can't understand how someone didn't go and implement FTS in Redis!

Upvotes: 0

soveran
soveran

Reputation: 890

What you want to do is not possible, but if your plan is to match prefixes, like in an autocomplete, you can take a look at sorted sets and ZRANGEBYLEX. You can take a look at this example. Even though it's not working right now, the code is very simple.

Upvotes: 1

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