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Memory cache eviction is inefficient and error-prone

    • Closed Issue created by Hazelnoot @fEmber

    What happened?

    Memory cache eviction is currently based on a hardcoded 3-minute timer. When the timer ticks, the cache loops through all entries and removes those that have been evicted. This has a few issues:

    1. The 3-minute interval adds considerable jitter to eviction times. Some caches have lifetimes as short as 10 minutes, which translates to a 30% margin of error.
    2. The full loop wastes CPU resources on the larger caches, like user & key.
    3. If the cache is not properly disposed, then it creates a memory leak and timer leak.

    As a solution, I propose that the implementation be modified to create a new timer per entry. When the timer ticks, it removes the associated row without any loops or checks. The timer ID can be stored within the cache entry and automatically cancelled when the entry is deleted. This has three benefits:

    1. Eviction timing is much more accurate.
    2. The full loop is removed.
    3. If the cache is not disposed, then all entries will slowly evict until the cache is empty. Then it will be garbage collected.

    Additional discussion: Misskey issue #14311.

    What did you expect to happen?

    Cache eviction should not consume significant system resources.

    Version

    v2024.6.0-dev (change was introduced in March 2021)

    Instance

    N/A - affects all instances

    What type of issue is this?

    backend

    How do you deploy Sharkey on your server? (Server-side issues only)

    N/A - affects all deployment methods

    What operating system are you using? (Server-side issues only)

    N/A - affects all operating systems

    Relevant log output N/A - this code does not produce logs

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    • I agree to follow this project's Contribution Guidelines
    • I have searched the issue tracker for similar issues, and this is not a duplicate.
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