【高级技巧】TTL缓存失效：容量与时效双阈值策略

local cache = { data = {}, cap = 1000, ttl = 300 }
local function cacheGet(actorName)
    local e = cache.data[actorName]
    if e == nil then
        return nil
    end
    if os.time() >= e.expire then
        cache.data[actorName] = nil
        return nil
    end
    return e.value
end
local function cacheSet(actorName, value)
    local now = os.time()
    cache.data[actorName] = { value = value, expire = now + cache.ttl }
    local n = 0
    for k, e in pairs(cache.data) do
        n = n + 1
        if now >= e.expire then
            cache.data[k] = nil
            n = n - 1
        end
    end
    while n > cache.cap do
        local oldestKey, oldest = nil, math.huge
        for k, e in pairs(cache.data) do
            if e.expire < oldest then
                oldest, oldestKey = e.expire, k
            end
        end
        if oldestKey == nil then
            break
        end
        cache.data[oldestKey] = nil
        n = n - 1
    end
end

local function getPlayerInfo(actorName)
    local hit = cacheGet(actorName)
    if hit then
        return hit
    end
    local info = loadInfoFromDB(actorName)
    cacheSet(actorName, info)
    return info
end