• Stan Hu's avatar
    Use process-wide memory cache for feature flags · f2c063d1
    Stan Hu authored
    When we switched from a single-threaded application server (Unicorn) to
    a multithreaded one (Puma), we did not realize that Puma often reaps
    threads after a request is done and recreates them later. This makes the
    thread-local cache ineffective, as the cache does not store anything
    beyond the lifetime of the thread.
    
    Since `ActiveSupport::Cache::MemoryStore` is thread-safe, we should be
    able to switch the L1 cache for feature flags to use this to reduce load
    on Redis.
    
    Since read and write access is synchronized, this does have the side
    effect of adding contention when feature flags are accessed.
    
    Discovered in
    https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/9414
    f2c063d1