TTL = Infinity

[marcopeg]

Hello and thanks for this package.

I'd like to propose that TTL could be set to Infinity pretty much same as for the max config param.
This would let setting some items as "pinned" into a TTL cache mechanism.

Thanks again,
Marco

[isaacs]

Idk, kinda sounds like a footgun. If you want an item that doesn't have a TTL, better off using a Map or plain old object instead of a cache that keeps things sorted by expiration.

More to the point, it would require a different data structure internally to do that. This module is able to efficiently prune by taking advantage of the fact that V8 keeps numeric object keys sorted. If a value's TTL is Infinity, then its expiration is also Infinity, which would be cast to the string 'Infinity', and then it'd need a bunch of special case logic to detect non-numeric expiration values. Not really a fit, sorry.

[isaacs]

Actually this might not be so bad. It does reduce performance a bit to have the string 'Infinity' in the TTL object, which I'm guessing is owing to it no longer being an object with strictly numeric keys. But it does the right thing without much added complexity. Adding the footgun!

[isaacs]

Actually I can do it without having 'Infinity' in the ttl object, it's faster to have the extra check and not take the deopt.

[marcopeg]

Hi Isaacs, thank you for considering this idea. I’m working on a distributed bottom-up data publisher in which each node is responsible for a small part of the data, but can cache data that is resolved by other nodes. I use ttlcache for this. The small “data that I own” is stored in the ttlcache object but should never expire. The rest is real cache. At the moment my implementation consists in re-setting the data on delete based on a flag in the record. I totally understand that mine is quite of a niche use case. But who knows… maybe it may turn to be useful to others as well. Thanks for the great tool. Marco