I recently start an online lesson on Geektime and come across an enlightening lecture from a facebook Product Manager Xiaoyin Qu. This article collects some learning & opinion that I thought useful.
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未来大学：文中的职场生命故事
受未来大学的邀请，我为未来大学的学员主讲了一期课程。其中有一段内容，是向学员介绍我的「职场故事」。我选择了「如何建立主动意识，明确方向快速蜕变」这个方向。
课程由北辰青年策划，课程内容由昕睿、文中共同完成创作。
Sim Cloud：蔚来服务云仿真平台设计
「一键加电」是蔚来为车主提供的代客加电服务。用户在 App 中下单后，系统的调度模式如下：用户下单后，调度系统会根据用户期望的取车位置 / 取车时间、车辆状态（例如续航里程）等因素，求解服务专员和服务电力资源的组合方案。系统在求解过程中会考虑一系列的地理信息因素（如限行围栏、道路状况等），然后结合服务人员的空闲情况、电力资源的服务能力和再生能力，以及系统的配置，求出服务距离、服务时长综合最优的服务方案。
为用户提供的加电资源主要有两种：换电站和移动充电车。换电站可以在 3 分钟内将旧电池拆下，换上新电池，提供非常好的加电体验。移动充电车则适合于远郊或低电量场景，除换电站和移动充电车以外，在部分资源还没有密集布局的地区，我们也会利用三方的充电桩进行加电服务。
以下是蔚来一键加电的服务流程图：
(其中虚线框表示服务流程，绿色段表示对资源的占用，蓝色段表示对服务专员的占用)。
随着车辆的逐渐交付，线上一键加电的订单需求日益增多。为保障一键加电的服务完成率和准时率，我们有大量的优化问题需要被解决，如：
- 预测 traffic model 的变化可能带来的服务时长、人员利用效率的影响
- 预测不同的人力和电力资源供给情况下，系统的服务能力上限
- 为服务人员的资源布局提出建议
- 评测待上线的算法和调参的效果
这些问题对系统的调度性能提出了离线和可测量要求。
对于包含调度行为的 O2O 系统，服务承载能力难以通过一个简单的模型或者线性公式进行数学推演，直接得出有参考意义的指标。为了更好地评测和调优系统，以及给出一线运营资源的配置建议，我们设计并实现了 Sim Cloud —— 一个可以精确重建线上系统和环境，引入线上流量或自定义流量，估算系统供需能力曲线、评估调度策略性能的仿真平台 。
Practical Apache Kafka Usage
I collect some of Apache Kafka usage in our team and write an internal post in Chinese. And I would like to pull the fundamental part into this post.
A 2D Nim Game
Intro
This article is about a Nim game I played in my primary school. The rule are simple:
- There are 16 stones, arranged in a 4 row * 4 column grid.
- Each player take stone(s) in turn.
- Once the stone is taken, there is a gap on it’s original location on the grid.
- In each take, one should take no more than 3 stones (1/2/3). Only those stones in the same row or in the same column without gap between them could be taken.
- Player who takes the last stone LOSE
Let me demonstrate it. Assuming 1 means there is stone on the specific cell and 0 represent a gap in the following chart. And those state that would definitely lose are called Losing State.
- the initial state could be represented as (I)
- the ending state could be represented as (II)
- one of the losing state (LS) for current turn player could be represented as (III)
1 | 1111 0000 0000 |
To be more specific, the following state is a possible game.
Understanding Fstab
Today I encounter a very strange problem that all recent deployed applications in a specific host fail to start, with a simple error message “Permission Denied. xxxx.sh could not be executed”.
Nonsense! They’ve run for a very long time with a Jenkins driven deployment, started by a deploy script. And a binary “could not be executed” might be controlled by user & file access flag. Both checked, using root user & 755 access flag.
Suddenly I remember that the hard-disk on this host have been re-mounted by Ops a few days ago, this operation might corrupt some filesystem runtime context. So I wrote a simple test script a.sh, place it into different mounting point /tmp and /data and try to execute them via ./a.sh (not bash ./a.sh because in this case we are using r way instead of x to access the script). And script could be executed under /tmp but not /data.
Seems we are close to the root cause, but what stop us from executing a binary in different mounting point? The answer is the fstab.
2017 Resolution
I drafted this new year resolution on the plane. Looking forwards to a fruitful year!
The Data Migration Problem
Today I am trying to solve a very interesting problem, I would like to call it the “data migration problem”.