# Redis Protocol Specification - Key Excerpts for Cache Client

**Authority Tier:** Tier 1 (Standards)
**Source:** https://redis.io/docs/reference/protocol-spec/ + https://redis.io/commands/
**Relevance:** Defines canonical behavior for TTL, eviction, key formats, and command semantics

---

## TTL and Expiration (SETEX, EXPIRE, EXPIREAT commands)

> **User fills in:** Fetch Redis command documentation for SETEX, EXPIRE, EXPIREAT
>
> Look for language like:
> - "SETEX key seconds value - Set key to hold string value with TTL of seconds"
> - "Keys are evicted when their TTL expires"
> - "If no expiration is set, keys persist indefinitely"

**Key Claims:**
- `cache/ttl :: required = true`
  - **Consequence:** Missing TTL causes memory leak - cached values never expire, unbounded growth

- `cache/ttl :: minimum = 1`
  - **Consequence:** TTL=0 means immediate expiration - cached value unusable

- `cache/expiration_strategy :: values = ["passive", "active"]`
  - **Consequence:** Wrong strategy affects memory vs CPU tradeoff

---

## Eviction Policies (MAXMEMORY-POLICY)

> **User fills in:** Fetch Redis documentation for `maxmemory-policy` configuration
>
> Look for:
> - LRU (Least Recently Used)
> - LFU (Least Frequently Used)
> - Random eviction
> - No eviction (return errors when memory full)

**Key Claims:**
- `cache/eviction_policy :: required = true`
  - **Consequence:** No eviction policy means undefined behavior when cache full (errors or random eviction)

- `cache/eviction_policy :: recommended = "LRU"`
  - **Consequence:** Wrong policy (e.g., random) degrades hit rates

- `cache/max_size :: required = true`
  - **Consequence:** Unbounded cache size causes OOM under sustained load

---

## Key Format and Validation

> **User fills in:** Fetch Redis documentation on key restrictions
>
> Look for:
> - Maximum key length (512 MB but practically much smaller)
> - Forbidden characters (control characters, null bytes)
> - Key naming best practices

**Key Claims:**
- `cache/key_validation :: required = true`
  - **Consequence:** Unvalidated keys enable injection attacks (control characters, escape sequences)

- `cache/key_length :: maximum = 1024`
  - **Consequence:** Excessively long keys waste memory and degrade performance

---

## Connection Semantics

> **User fills in:** Fetch Redis documentation on connection handling, pipelining, pooling
>
> Look for:
> - Connection persistence recommendations
> - Pipelining for performance
> - Connection pool sizing

**Key Claims:**
- `cache/connection_pooling :: required = true`
  - **Consequence:** No pooling means new connection per request - resource exhaustion

- `cache/connection_timeout :: minimum = 1`
  - **Consequence:** timeout=0 causes indefinite blocking on connection failures

---

## Extraction Guide

1. **Fetch documentation:**
   ```bash
   # Navigate to Redis official docs
   open https://redis.io/docs/
   ```

2. **Search for key sections:**
   - Commands: SETEX, EXPIRE, GET, SET
   - Configuration: maxmemory-policy, timeout
   - Best practices: Key design, connection management

3. **Extract MUST/SHOULD patterns:**
   - Look for normative language (MUST, SHOULD, SHALL)
   - Document consequences from "Common Pitfalls" sections
   - Note performance implications

4. **Map to concept paths:**
   - `cache/ttl`
   - `cache/eviction_policy`
   - `cache/key_validation`
   - `cache/connection_pooling`

5. **Add to claims with provenance:**
   - Provenance: "Redis Protocol Specification v7.0 - SETEX command"
   - Link to specific command or config doc