63 lines
2.0 KiB
Markdown
63 lines
2.0 KiB
Markdown
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---
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title: Use Hash Field Expiration for Per-Field TTL
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impact: MEDIUM
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impactDescription: Fine-grained expiration without managing timers
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tags: hash, expiration, ttl, hexpire
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description: Use Hash Field Expiration for Per-Field TTL
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alwaysApply: true
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---
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## Use Hash Field Expiration for Per-Field TTL
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Use hash field expiration (Redis 7.4+) to delete individual fields automatically from a hash after a specific period of time. This is useful for caching scenarios where different fields have different lifetimes, and is easier than managing expiration from your own code.
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**Correct:** Use HEXPIRE to set per-field TTL on hash fields.
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**Python** (redis-py):
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```python
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import redis
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client = redis.Redis(host='localhost', port=6379)
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# Set hash fields
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client.hset("sensor:sensor1", mapping={
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"air_quality": "256",
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"battery_level": "89"
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})
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# Set 60-second TTL on specific fields (Redis 7.4+)
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client.hexpire("sensor:sensor1", 60, "air_quality", "battery_level")
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```
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**Java** (Jedis):
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```java
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import redis.clients.jedis.UnifiedJedis;
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import java.util.Map;
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import java.util.HashMap;
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try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {
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Map<String, String> hashFields = new HashMap<>();
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hashFields.put("air_quality", "256");
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hashFields.put("battery_level", "89");
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jedis.hset("sensor:sensor1", hashFields);
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// Set 60-second TTL on specific fields (Redis 7.4+)
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jedis.hexpire("sensor:sensor1", 60, "air_quality", "battery_level");
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}
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```
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**When to use:**
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- Sensor data or metrics that become stale after a period
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- Session attributes where different fields have different lifetimes
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- Cached values within a hash that should auto-expire independently
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- Temporary flags or tokens stored alongside persistent data
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**When NOT needed:**
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- Persistent user profiles or configuration
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- Data where the entire hash should expire together (use `EXPIRE` on the key instead)
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- Fields managed by application logic with explicit deletion
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Reference: [HEXPIRE command](https://redis.io/docs/latest/commands/hexpire/)
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