56 lines
1.3 KiB
Markdown
56 lines
1.3 KiB
Markdown
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---
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title: Set TTL on Cache Keys
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impact: HIGH
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impactDescription: Prevents unbounded memory growth
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tags: ttl, expiration, cache, memory
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description: Set TTL on Cache Keys
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alwaysApply: true
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---
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## Set TTL on Cache Keys
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Always set expiration times on cache keys to prevent unbounded memory growth.
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**Correct:** Set TTL at write time.
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**Python** (redis-py):
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```python
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# Good: TTL set atomically with the value
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redis.setex("cache:user:1001", 3600, user_json)
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# Good: For hashes, set TTL after
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redis.hset("session:abc", mapping=session_data)
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redis.expire("session:abc", 1800)
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```
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**Java** (Jedis):
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```java
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import redis.clients.jedis.params.SetParams;
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// Good: TTL set atomically with SetParams
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jedis.set("cachedItem:1", "fe8c357903ac9", new SetParams().ex(120));
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```
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**Incorrect:** Forgetting TTL on cache keys.
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**Python** (redis-py):
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```python
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# Risk: This key may live forever
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redis.set("cache:user:1001", user_json)
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```
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**Java** (Jedis):
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```java
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// Risk: This key may live forever
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jedis.set("cachedItem:1", "fe8c357903ac9");
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```
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**TTL strategies:**
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- Cache data: 1-24 hours depending on freshness requirements
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- Sessions: 30 minutes to 24 hours
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- Rate limiting: Seconds to minutes
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- Temporary locks: Seconds with automatic release
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Reference: [Redis EXPIRE](https://redis.io/commands/expire/)
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