【数据存储】大表瘦身：日志表的滚动清理方案

---全局定时器 41 号：每 30 分钟执行一轮
setontimerex(41, 1800)
function LogRoll.tick()
    local cutoff = os.date("%Y%m%d", os.time() - 90 * 86400)
    local oldest = LogRoll.oldestDay()
    if oldest >= cutoff then return end
    LogRoll.archiveDay(oldest)
end

function LogRoll.archiveDay(day)
    DB.trans(function()
        DB.exec("INSERT INTO logs_archive SELECT * FROM logs WHERE day = ?", day)
        DB.exec("DELETE FROM logs WHERE day = ?", day)
    end)
end

---归档行数与删除行数的对账
function LogRoll.verify(day)
    local archived = DB.scalar("SELECT COUNT(*) FROM logs_archive WHERE day = ?", day)
    local remained = DB.scalar("SELECT COUNT(*) FROM logs WHERE day = ?", day)
    if remained > 0 or archived == 0 then
        LogRoll.alert("归档对账失败: " .. day)
        return false
    end
    LogRoll.markDone(day)
    return true
end