Can I listen event on lpush operation of Redis?

Question

I am using Jedis java client for redis. My requirement is that when someone add item to list, say mylist by doing jedisClient.lpush("mylist", "this is my msg"), I need to get notification. Is this possible ?

Answer 1

Yes, it is possible to achieve that in one of two ways.

The first approach is to use Redis' keyspace notifications. Configure Redis to generate list events with the following configuration directive:

CONFIG SET notify-keyspace-events El

Then, subscribe to the relevant channel/channels. If you want to subscribe only to mylist's changes, do:

SUBSCRIBE __keyevent@0__:mylist

Or, use PSUBSCRIBE and listen to events to matching key names that match a pattern.

Note, however, that keysapce notifications will not provide the actual pushed value. You can use Lua scripts as an alternate approach and implement your own notifications mechanism. For example, use the following script to push and publish a custom message to a custom channel:

local l = redis.call("LPUSH", KEYS[1], ARGS[1])
redis.call("PUBLISH", "mylistnotif:" .. KEYS[1], "Pushed value " .. ARGS[1])
return l

Make sure that "someone" uses that script to do the actual list-pushing and subscribe to the relevant channel/channels.