Additional Keyspace Notification Info

[sra...@gmail.com]

I have a sorted set, and when elements are removed using zrem, I need to know which elements were removed and what their scores were.

1. Is this supported by redis keyspace notifications?

2. If not, can anyone suggest a way to implement this functionality?

Thanks

[Itamar Haber]

Hi,

WRT 1 - no, it isn't. The keyspace notifications generated by Redis in general, and specifically for ZREM command, do not include the actual data - only the key's name and command.

WRT 2 - the easiest way of doing this is to use the PUBLISH command alongside calling ZREM. The following Lua script, for example, does this:

    for _, arg in pairs(ARGV) do

        local score = redis.call('ZSCORE', KEYS[1], arg)

        redis.call('PUBLISH', 'mychannel', 'key: ' .. KEYS[1] .. ', element: ' .. arg .. ', score: ' .. tostring(score))

    end

    redis.call('ZREM', KEYS[1], unpack(ARGV))

Assuming that this script is loaded to Redis (the SCRIPT LOAD command), you can call it as follows: EVALSHA <script-sha> 1 <zset-keyname> <1st element to remove> <2nd element> ....

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