life-echo/api/.agents/skills/redis-development/rules/conn-blocking.md

title, impact, impactDescription, tags, description, alwaysApply

title	impact	impactDescription	tags	description	alwaysApply
Avoid Slow Commands in Production	HIGH	Prevents Redis from becoming unresponsive	slow-commands, keys, scan, performance	Avoid Slow Commands in Production	true

Avoid Slow Commands in Production

Some Redis commands are slow because they scan large datasets. Use incremental alternatives to avoid blocking the server.

Avoid	Use Instead
KEYS *	SCAN with cursor
SMEMBERS on large sets	SSCAN
HGETALL on large hashes	HSCAN
LRANGE 0 -1 on large lists	Paginate with LRANGE 0 100

Correct: Use SCAN for iteration.

Python (redis-py):

# Good: Non-blocking iteration
cursor = 0
while True:
    cursor, keys = redis.scan(cursor, match="user:*", count=100)
    for key in keys:
        process(key)
    if cursor == 0:
        break

Java (Jedis):

import redis.clients.jedis.ScanIteration;
import redis.clients.jedis.UnifiedJedis;
import java.util.List;

try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {
    // ScanIteration manages the cursor automatically
    ScanIteration scan = jedis.scanIteration(10, "user:*", "hash");

    while (!scan.isIterationCompleted()) {
        List<String> result = scan.nextBatch().getResult();
        for (String key : result) {
            process(key);
        }
    }
}

Incorrect: Using KEYS in production.

Python (redis-py):

# Bad: Scans all keys, slow on large datasets
keys = redis.keys("user:*")

Java (Jedis):

// Bad: Scans all keys, blocks the server
Set<String> result = jedis.keys("*");

Note: Truly blocking commands (like BLPOP, BRPOP, BLMOVE) that wait indefinitely for data are appropriate for some use cases like job queues, but should be used with timeouts.

# Blocking pop with timeout - appropriate for queue consumers
result = redis.blpop("task_queue", timeout=5)

Reference: Redis SCAN