feat(benchmark): M1 IMU 高频摄入压测（引擎层）+ 诚实结果

[NeverENG]

M1 第一步：用开环压测验证存储引擎能否扛住高频传感器摄入。落点 benchmark/ingest/（独立 package，不动现有 benchmark/）+ docs-step/ 方案与结果。

做了什么

• 饱和相（闭环打满）找峰值写速率；开环相（定速率、有界队列、满即丢帧）证定速率丢帧/尾延迟/内存。

诚实结果（经 60s 复测修正）

• 峰值写速率 ~2.0M w/s，但打满时内存无界（heap 1.5GiB）。
• 内存在 50k–200kHz 下都随时间持续增长，60s 无平稳态（短跑 6s 的"内存有界"是错觉）。
• 丢帧经核为队列深度/Windows 计时毛刺，非引擎极限（500kHz 大队列下丢帧归零）。

抓到的真问题

MemTable 写入无背压（StartFlush 非阻塞、Put 永不阻塞）+ SSTable/bloom 元数据累积 → "内存封顶"在持续负载下不成立。下一项存储改进：加写背压，再附"前后内存随时间曲线"。

详见 docs-step/M1-ingest-benchmark-result.md。

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Reviewing files that changed from the base of the PR and between fb0d53c and 3549336.

📒 Files selected for processing (3)

• benchmark/ingest/main.go
• docs-step/M1-ingest-benchmark-plan.md
• docs-step/M1-ingest-benchmark-result.md

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/m1-ingest-benchmark

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[github-actions]

🐯 BanGD 数据库内核评审

整体风险：🟢 低

变更总结：该 PR 新增 benchmark/ingest/ 压测程序，用于在引擎层（A1）验证 BanDB 存储引擎能否扛住高频传感器摄入。核心设计是开环（open-loop）模型：生产者以固定速率通过有界 channel 投递样本、队列满即丢帧；饱和相（闭环打满）测峰值写吞吐。PR 同时产出 docs-step/M1-ingest-benchmark-plan.md（方案说明）和 docs-step/M1-ingest-benchmark-result.md（诚实结果）。PR 不动存储引擎本身的代码，仅扩展压测框架，但结果文档抓到了引擎层的一个关键架构问题——MemTable 写入无背压、Put 永不阻塞，导致内存在持续负载下无界增长。

本评审不阻塞合入；架构级建议以 Issue 形式跟踪，普通问题在下方内联列出。

未发现需要从架构层面改进的问题。

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