77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
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---
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title: Use INCR for Atomic Counters
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impact: MEDIUM
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impactDescription: Atomic increment avoids race conditions
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tags: incr, counters, atomic, performance
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description: Use INCR for Atomic Counters
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alwaysApply: true
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---
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## Use INCR for Atomic Counters
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If a string represents an integer value, use the `INCR` command to increment the number directly. The increment is atomic and always returns the new value. Use `INCRBY` to increment by any integer (positive or negative). This is more efficient and race-condition-free than reading, incrementing in code, and writing back.
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**Correct:** Use INCR/INCRBY for atomic counter updates.
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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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# Initialize counter
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client.set("counter", "0")
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# Atomic increment - returns new value
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new_value = client.incr("counter") # Returns 1
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# Increment by specific amount
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new_value = client.incrby("counter", 10) # Returns 11
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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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try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {
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jedis.set("counter", "0");
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// Atomic increment - returns new value
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long newValue = jedis.incr("counter"); // Returns 1
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// Increment by specific amount
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newValue = jedis.incrBy("counter", 10); // Returns 11
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}
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```
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**Incorrect:** Read-modify-write pattern creates race conditions.
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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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client.set("counter", "0")
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# BAD: Race condition - another client could modify between GET and SET
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curr_value = int(client.get("counter"))
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client.set("counter", str(curr_value + 1)) # Not atomic!
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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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try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {
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jedis.set("counter", "0");
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// BAD: Race condition between GET and SET
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long currValue = Long.parseLong(jedis.get("counter"));
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jedis.set("counter", Long.toString(currValue + 1)); // Not atomic!
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}
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```
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Reference: [INCR command](https://redis.io/docs/latest/commands/incr/)
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