I need to store strings and associate a unique integer to each one. The integer must be as short/small as possible . Is it possible to do that in Redis? Basically I need something like SADD but instead to return the number of elements in the set I need it to return the index of the element inserted(newly stored or existing).
Pseudo code:
// if mystring already exists in myset it returns its index
// otherwise stores it and returns its index.
index := storeOrReturnIndex(myset, mystring)
Would using a hashmap cover what you are looking for?
> HSET hashmap 0 "first string"
(integer) 1
> HSET hashmap 1 "second string"
(integer) 1
> HSET hashmap 2 "third string"
(integer) 1
> HGET hashmap 1
"second string"
> HLEN hashmap
3
You can store the last modified index in a key with:
> SET last_modified 1
Then retrieve it with:
> GET last_modified
You can use the Redis INCR command to atomically acquire a new, unique index.
Pattern: Counter
The counter pattern is the most obvious thing you can do with Redis atomic increment operations. The idea is simply send an INCR command to Redis every time an operation occurs. For instance in a web application we may want to know how many page views this user did every day of the year. To do so the web application may simply increment a key every time the user performs a page view, creating the key name concatenating the User ID and a string representing the current date. This simple pattern can be extended in many ways:
So use INCR to get the next unique, smallest index in an atomic way wherever you want to store a new item (URL). Then you can use HSET to store the index associated with your item, and HGET to get the associated index for an item.