42 lines
1.3 KiB
Markdown
42 lines
1.3 KiB
Markdown
---
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title: "Per-Index Time Decay"
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created: 2026-06-24
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updated: 2026-06-24
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type: concept
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tags: ["information-retrieval", "agent-memory", "decay", "elasticsearch"]
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sources:
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- "[[atlas-agent-memory-architecture-2026]]"
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---
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# Per-Index Time Decay
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Per-Index Time Decay 是 Atlas 记忆系统中每个索引使用独立衰减策略的设计：episodic 按 timestamp 衰减，semantic 按 last_used_at 衰减并受 use_count boost，procedural 豁免衰减（1.0）。
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## 衰减函数
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Gauss 衰减 + offset 平坦区 + use_count boost：
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```
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decay = exp(-pow(max(days - offset, 0) / scale, 2) * log(sqrt(2)))
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// semantic 额外: decay *= 1 + log10(1 + use_count) * use_count_boost
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// procedural: decay = 1.0
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```
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## 关键参数
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| 参数 | 默认值 | 含义 |
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|------|--------|------|
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| DECAY_SCALE | 1825d (~5年) | 衰减半衰期，客服应收紧至 60-180d |
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| DECAY_OFFSET | 180d | 平坦区，offset 内 doc 乘数 1.0 |
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| USE_COUNT_BOOST | 0.2 | use_count=10 → ~1.21x, =100 → ~1.40x |
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## 设计原则
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信息的衰减驱动力是它有多频繁被需要，不是它有多旧。
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- semantic 用 last_used_at 而非 timestamp：一个三年前的稳定偏好如果一直在被用到，不应衰减
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- procedural 豁免衰减：操作流程不因时间失效
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## 参考
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- [[atlas-agent-memory-architecture-2026]]
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- [[agent-memory-taxonomy]]
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