Lua script excution failing with "attempt to compare number with nil"

[gl...@telecave.net]

Hi,

 

Sporadically, Redis fails executing following Lua script:

 

var newDeadlineDouble = newDeadline.UtcDateTime.ToOADate();

 

var timeoutslist = someRedisSortedSetkey;

double score = some_score_from_querying_above_sortedset;

double scoremin = score - 0.000000000004; // double number encoding/parsing produces some inconsistencies requiring a range for comparison

double scoremax = score + 0.000000000004;

var id = somerediskey;

 

var script = "local score = tonumber(redis.call('zscore', '" + timeoutslist + "', KEYS[1]))\n" +

             "if score > tonumber(ARGV[1]) and score < tonumber(ARGV[2]) then redis.call('zadd', '" + timeoutslist + "', ARGV[3], KEYS[1]) return redis.call('hgetall', KEYS[2]) end";

 

var task = db.ScriptEvaluateAsync(script, new RedisKey[] { id, id }, new RedisValue[] { scoremin, scoremax, newDeadlineDouble });

await task.ConfigureAwait(false);

 

Exception:

StackExchange.Redis.RedisServerException: ERR Error running script (call to f_2bb5d9f8f933748c46de66a1b175e89c339533e5): @user_script:2: user_script:2: attempt to compare number with nil

 

I don’t see how any comparison could run into nil.

Is this a known issue?

Any suggestions for a workaround, please?

 

This issue happens infrequently (about 10x a day) in multiple environments under some moderate load against Redis (Window) 3.0.500, but I have seen already in earlier versions.

Regards,

Gunter

[Marc Gravell]

My immediate assumption would be that this happens when the parent key (someRedisSortedSetKey) doesn't exist, or has no member with the field name from KEYS[1] (id). You may want to check what comes back from zscore against nil here.

As side notes:

- a member name inside a sorted set is not a "key" in this context, and should be passed as an ARGV

- the parent key name **is** a "key" in this context, and should be passed in KEYS, not concatenated into the command

Getting these confused won't necessarily hurt you *now*, but it would be a blocker on "cluster", as it'll make commands go to the wrong servers. Additionally, you might want to like at "verbatim string literals" in C#, which allow you to write multi-line strings very conveniently, for example:

const string myLuaCommand=@"do this

and this

and another line here";

Marc

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Regards,

Marc