key expiry and ttl during the evaluation of lua scripts

[halaei]

As far as I know, these behaviors are not documented:

1. If a key with expiry (ttl) exists at the start of eval, it will not get expired during the evaluation of a script.
2. During the evaluation of a lua script, ttl of a key can go down to zero. After that, it remains zero until the script terminates.
3. To have logic based on the value of ttl can violate the concept of scripts as pure functions.

[halaei]

I think it would be better if ttl was constant during script evaluation.

[itamarhaber]

@halaei the points you've raised are good and, IMO, should be included in EVAL's documentation.

As for keeping ttls constant during script execution, I think that suggestion belongs in the https://github.com/antirez/redis repository. While I see your point in suggesting it, it would be a breaking change in terms of behavior, so I'd be hesitant about it.

[zuiderkwast]

Fixed in redis/redis#10300. Time is now frozen during script exection. Regarding the points:

1. If a key with expiry (ttl) exists at the start of eval, it will not get expired during the evaluation of a script.

This is still true.

2. During the evaluation of a lua script, ttl of a key can go down to zero. After that, it remains zero until the script terminates.

Not true anymore. The TTL of a key doesn't change during script execution.

3. To have logic based on the value of ttl can violate the concept of scripts as pure functions.

Not true anymore.