life-echo/api/.agents/skills/redis-development/rules/data-incr.md

title, impact, impactDescription, tags, description, alwaysApply

title	impact	impactDescription	tags	description	alwaysApply
Use INCR for Atomic Counters	MEDIUM	Atomic increment avoids race conditions	incr, counters, atomic, performance	Use INCR for Atomic Counters	true

Use INCR for Atomic Counters

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.

Correct: Use INCR/INCRBY for atomic counter updates.

Python (redis-py):

import redis

client = redis.Redis(host='localhost', port=6379)

# Initialize counter
client.set("counter", "0")

# Atomic increment - returns new value
new_value = client.incr("counter")  # Returns 1

# Increment by specific amount
new_value = client.incrby("counter", 10)  # Returns 11

Java (Jedis):

import redis.clients.jedis.UnifiedJedis;

try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {
    jedis.set("counter", "0");
    
    // Atomic increment - returns new value
    long newValue = jedis.incr("counter");  // Returns 1
    
    // Increment by specific amount
    newValue = jedis.incrBy("counter", 10);  // Returns 11
}

Incorrect: Read-modify-write pattern creates race conditions.

Python (redis-py):

import redis

client = redis.Redis(host='localhost', port=6379)

client.set("counter", "0")

# BAD: Race condition - another client could modify between GET and SET
curr_value = int(client.get("counter"))
client.set("counter", str(curr_value + 1))  # Not atomic!

Java (Jedis):

import redis.clients.jedis.UnifiedJedis;

try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {
    jedis.set("counter", "0");
    
    // BAD: Race condition between GET and SET
    long currValue = Long.parseLong(jedis.get("counter"));
    jedis.set("counter", Long.toString(currValue + 1));  // Not atomic!
}

Reference: INCR command