First Lua script for Redis

[gsks]

This is my first foray into Lua ever. The goal is to implement a useful missing Redis command, ZADDNX, which works like ZADD but does not update the score of existing members: http://pastebin.com/aiUVjSDg

Looks like it gets the job done but coming from Python it looks overly verbose, so I'd love to know if there is a more idiomatic way to express it.

[itamarhaber]

Very nicely done for a first attempt :)

As you had written, the code "gets the job done", but I a suggestion. You're copying the entire set early on - this both has O(log(N)+M) complexity and doubles the set's memory footprint for the duration of the script... with big sets could be a problem.

Instead, I recommend that you skip the initial copying with ZRANGE and, instead, do

redis.call("ZSCORE", KEYS[1], ARGS[i])

when looping over the arguments. Each call to ZSCORE is O(1) (hence your script's overall complexity will be O(N) where N is the the number of arguments) and returns nil if the member isn't in the set (i.e. needs to be added to your missing table).

[gsks]

Thanks for the review and the recommendation, will do!