【高级技巧】金丝雀发布：小流量验证的阶梯放量封装

local canary = { ratio = 5, oldFn = nil, newFn = nil,
    errCount = 0, callCount = 0 }
local function bucketOf(name)
    local h = 0
    for i = 1, #name do
        h = (h * 31 + string.byte(name, i)) % 100
    end
    return h
end
local function dispatch(name, ...)
    canary.callCount = canary.callCount + 1
    if bucketOf(name) < canary.ratio then
        local ok, a, b = pcall(canary.newFn, name, ...)
        if not ok then
            canary.errCount = canary.errCount + 1
        end
        return a, b
    end
    return canary.oldFn(name, ...)
end
local function shouldRollback()
    if canary.callCount < 200 then
        return false
    end
    return canary.errCount / canary.callCount > 0.02
end

local STEPS = { 5, 25, 50, 100 }
if shouldRollback() then
    canary.ratio = 0
    print("错误率超 2%，已回退旧脚本")
end