Spring-session: why RedisSessionExpirationPolicy#onDelete remove something not exist in the expirations SET?

[Alwayswithme]

the spring:session:expirations:${roundUpToNextMinute} redis SET is store value call keyToExpire:

        String expireKey = getExpirationKey(toExpire);
        BoundSetOperations<Object, Object> expireOperations = this.redis.boundSetOps(expireKey);
        expireOperations.add(keyToExpire);

the keyToExpire is a string like expires:${sessionId}
https://github.com/spring-projects/spring-session/blob/927008bdc89701555f2f8f900f4f898df23b1476/spring-session-data-redis/src/main/java/org/springframework/session/data/redis/RedisSessionExpirationPolicy.java#L97

however, when delete the session, it actually remove the session id not expires:${sessionId}

    this.redis.boundSetOps(expireKey).remove(session.getId());

https://github.com/spring-projects/spring-session/blob/927008bdc89701555f2f8f900f4f898df23b1476/spring-session-data-redis/src/main/java/org/springframework/session/data/redis/RedisSessionExpirationPolicy.java#L70

Is this a defact or My misunderstanding?

[vpavic]

The behavior of session expiration handling for Redis session repository is described both in the RedisOperationsSessionRepository javadoc and reference manual.

Are you experiencing any particular issue here?

[Alwayswithme]

Thank you for reply, I know Spring Redis will create 3 key in redis.

1. the session, a redis HASH, which key is spring:session:sessions:${sessionId}
2. the session expireKey, a redis STRING, which key is spring:session:sessions:expires:${sessionId}
3. the set for tracking session expireKey, and then add expires:${sessionId} to the nearest minute set, a redis SET, which key is spring:session:expirations:${roundUpToNextMinute} .

when delete a session, the second key will be delete, right?

https://github.com/spring-projects/spring-session/blob/085554f56b0ee7c96d45a49daa1c664db5fb1184/spring-session-data-redis/src/main/java/org/springframework/session/data/redis/RedisIndexedSessionRepository.java#L484

And I found that SET still tracking the expireKey. Then I dont understand why not just remove expires:${sessionId} in the third key.

And I see the code, notice that RedisSessionExpirationPolicy#onDelete methond remove the ${sessionId} instead of expires:${sessionId} from the redis SET. but ${sessionId} will never add to the SET.
https://github.com/spring-projects/spring-session/blob/085554f56b0ee7c96d45a49daa1c664db5fb1184/spring-session-data-redis/src/main/java/org/springframework/session/data/redis/RedisSessionExpirationPolicy.java#L70
So I create this issue. I think it's ok to clean up this element in the set. By change this line to something like:

this.redis.boundSetOps(expireKey).remove("expires:" + session.getId());

My English is not very good, hope you can understand what I mean.

[Alwayswithme]

@vpavic please take a look

[eleftherias]

Thanks for the report @Alwayswithme.
I'm going to close this issue as a duplicate of gh-585.
Please follow gh-585 for updates.