今日固定时间表
08:30 wake 只保留起床；学习从 08:50 开始。三块窗口不互相挤占。
| 08:30 wake | 起床、早餐、准备白板；不安排预读或算法。 |
|---|---|
| 08:50—09:20 | 08:50—10:55 system design 盲做 — 不看原文，独立画 media metadata + feed fan-out + CDN render path。 |
| 09:20—09:50 | 08:50—10:55 system design 精确原文 — 读 Instagram visible live inventory 全部 anchors，记录 premium gate 之外可验证范围。 |
| 09:50—10:25 | 08:50—10:55 system design 迁移差异 — 对比 News Feed/Live Comments：需求变化、失效复用、新瓶颈、浅层迁移追问。 |
| 10:25—10:55 | 08:50—10:55 system design transfer close — 输出 8 分钟 Instagram transfer answer，不重讲 News Feed 原图。 |
| 14:30—16:15 | NeetCode Tag · Stack 三道题在下方独立算法表执行，避免系统设计表格挤压算法细节。 |
| 20:30—21:15 | 20:30—21:15 Instagram 迁移口述：先讲盲做版本，再讲读完 live heading 后改了什么。 |
算法模块
连续单一 NeetCode Stack tag；每天 3 题，14:30—16:15 完成。
| # | Problem | Invariant focus | 执行 |
|---|---|---|---|
| 13 | Car Fleet | 限时复盘：同位置/同到达时间。 | 35 分钟限时 + 5 分钟 invariant/bug risk |
| 14 | Largest Rectangle in Histogram | 限时复盘：哨兵柱清栈。 | 35 分钟限时 + 5 分钟 invariant/bug risk |
| 15 | Valid Parentheses | mock 前热身：栈空访问。 | 35 分钟限时 + 5 分钟 invariant/bug risk |
闭卷起手
先暴露自己的当前模型，再用 live headings 修正。
30 分钟盲做 Instagram：photo/video post、follow、chronological feed、media upload/render。写下三条复用假设，再主动打破它们。
Hello Interview 精确目录
day 页面必须链接到具体 section anchors；周级 overview 不放小节链接。
| 项目 | 精确 section anchor | Disposition | 今天怎么用 |
|---|---|---|---|
| Understanding the Problem | required reading | transfer problem, read after blind design | |
| Functional Requirements | required reading | photo/video posts, follow, chronological feed | |
| Non-Functional Requirements | required reading | instant media render and 500M DAU | |
| The Set Up | required reading | scope limits | |
| Defining the Core Entities | required reading | User, Post, MediaAsset, Follow, FeedItem | |
| API or System Interface | required reading | upload/init, create post, get feed | |
| High-Level Design | required reading | metadata feed plus media data plane | |
| 1. Users should be able to create posts featuring photos, videos, and a simple caption | required reading | media processing state machine | |
| 2. Users should be able to follow other users | required reading | same graph shape, different fan-out payload | |
| 3. Users should be able to see a chronological feed of posts from the users they follow | required reading | feed hydration with media metadata | |
| Potential Deep Dives | deep dive | transfer pressure | |
| 1) The system should deliver feed content with low latency (< 500ms) | deep dive | feed cache, metadata hydration and pagination | |
| 2) The system should render photos and videos instantly, supporting photos up to 8MB and videos up to 4GB | deep dive | blob/metadata separation, thumbnails, CDN, transcode | |
| 3) The system should be scalable to support 500M DAU | deep dive | large-scale feed fan-out plus media delivery | |
| What is Expected at Each Level? | level expectation | calibrate transfer answer | |
| Mid-level | level expectation | adapt basic feed | |
| Senior | level expectation | identify changed bottlenecks | |
| Staff+ | level expectation | challenge invalid reuse assumptions |
DDIA 精确决策卡
只读能改变今天设计决定的小节。
| 项目问题 | 精确 DDIA subsection | 改变的系统决定 |
|---|---|---|
| Instagram feed 迁移时，media metadata cache 是什么派生视图？ | Ch13 · 物化视图和缓存 | feed row 只携带 post/media pointers；thumbnail/transcode/CDN metadata 是派生读模型，必须能从 media pipeline 重建。 |
今日产出与修复规则
| 课程角色 | TRANSFER · blind first then live-source read |
|---|---|
| 必须交付 | Instagram transfer memo：changed requirements、invalid reuse assumptions、new bottlenecks、shallow-transfer follow-ups。 |
| 修复规则 | 如果只把 News Feed 的 Post 换成 Photo，补 media upload state、transcoding/CDN、thumbnail readiness 和 render SLO。 |
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