Remove Redis key deletion behavior on expiration - redis

Question

I'm using Redis Key Space Notification to get my application notified when a specified key gets expired.
But when the key gets expired, Redis deletes the key, i need to remove this behavior because my application can use this expired information in another moment.
Is there a way to remove this behavior?

Answer 1

As #sazzad and #nitrin0 said, there's no way to change that.
As another option to get a similar result, I'd suggest you use a sorted set to track these "psuedo-expirations", and when they "expire", a background process does whatever else you need the key for: move it, transform it, reset the expiration, etc.
Use the command zadd to both create a new sorted set and to add members to it. The key for the set can be anything, but I'd use the members as the keys from the data that expires so you can easily work with both the real data, and the member in the sorted set.
ZADD name-of-sorted-set NX timestamp-when-data-expires key-of-real-data
Let's break this down:
name-of-sorted-set is what you'd use in the other Z* commands to work with this specific sorted set.
NX means "Only add new elements. Don't update already existing elements.". The other option is XX which is "Only update elements that already exist. Don't add new elements." For this, the only options are NX or nothing.
timestamp-when-data-expires is the score for this member, and we'll use it as the exact timestamp when the data would otherwise "expire", so you'll have to do some calculations in your application to provide the timestamp instead of just the seconds until it expires.
key-of-real-data is the exact key used for the real data this represents. Using the exact key here will help easily combine the two when you're working with this sorted set to find which members have "expired", since the members are the keys you'd use to move, delete, transform, the data.
Next I'd have a background process run zrangebyscore to see if there are any members whose scores (timestamps) are within some range:
ZRANGEBYSCORE name-of-sorted-set min-timestamp max-timestamp WITHSCORES LIMIT 0 10
Let's break this down too:
name-of-sorted-set is the key for the set we chose in ZADD above
min-timestamp is the lower end of the range to find members that have "expired"
max-timestamp is the higher end of the range
WITHSCORES tells Redis to return the name of the members AND their scores
LIMIT allows us to set an offset (the 0) and a count of items to return (the 10). This is just an example, but for very large data sets you'll likely have to make use of both the offset and count limits.
ZRANGEBYSCORE will return something like this if using redis-cli:
1) "first-member"
2) "1631648102"
3) "second-member"
4) "1631649154"
5) "third-member"
6) "1631650374"
7) "fourth-member"
8) "1631659171"
9) "fifth-member"
10) "1631659244"
Some Redis clients will change that, so you'll have to test it in your application. In redis-cli the member-score pair is returned over two lines.
Now that you have the members (keys of the actual data) that have "expired" you can do whatever it is you need to do with them, then probably either remove them from the set entirely, or remove them and replace them. Since in this example we created the sorted set with the NX example, we can't update existing records, only insert new ones.