redis expire is effective on key level, not id level

[cyh-ustc]

i assume the expire is for some id somehow not released
however the expire is effective on key level but not id level
which means if there are continuous requests, the expire setting has no effect

[PatrickTaibel]

The limit_expire setting is just for ensuring that the used key gets cleaned up eventually. In case of continuous use of one key there is nothing to be cleaned up. The actual concurrency instance gets removed by the context manager during exit.