Backend Engineering Snippets (Redis, Kafka, SQL)

Redis Caching

Basic Set/Get (CLI)

redis-cli SET user:1 '{"name": "John"}' EX 3600
redis-cli GET user:1

Check Memory Usage

redis-cli info memory

Clear All Cache

redis-cli flushall

Monitor Commands in Real-time

redis-cli monitor

Apache Kafka

Create a Topic

kafka-topics.sh --create --topic my-topic --bootstrap-server localhost:9092 --partitions 3 --replication-factor 1

Produce Messages (CLI)

kafka-console-producer.sh --topic my-topic --bootstrap-server localhost:9092

Consume Messages (CLI)

kafka-console-consumer.sh --topic my-topic --from-beginning --bootstrap-server localhost:9092

Check Consumer Group Offsets

kafka-consumer-groups.sh --bootstrap-server localhost:9092 --group my-group --describe

PostgreSQL Optimization

Explain Analyze

Understand how a query is executed.

EXPLAIN ANALYZE SELECT * FROM orders WHERE customer_id = 123;

Find Slow Queries

SELECT query, calls, total_exec_time, rows
FROM pg_stat_statements
ORDER BY total_exec_time DESC
LIMIT 10;

Check Table Size

SELECT relname AS "Table",
       pg_size_pretty(pg_total_relation_size(relid)) AS "Size"
FROM pg_catalog.pg_statio_user_tables
ORDER BY pg_total_relation_size(relid) DESC;

Kill Long Running Query

SELECT pg_terminate_backend(pid)
FROM pg_stat_activity
WHERE state = 'active'
  AND now() - query_start > interval '5 minutes';

Microservices Patterns

Circuit Breaker (Resilience4j)

CircuitBreakerConfig config = CircuitBreakerConfig.custom()
    .failureRateThreshold(50)
    .waitDurationInOpenState(Duration.ofMillis(1000))
    .build();

CircuitBreaker registry = CircuitBreaker.of("myService", config);

Retry Pattern

RetryConfig config = RetryConfig.custom()
    .maxAttempts(3)
    .waitDuration(Duration.ofMillis(500))
    .build();

Retry retry = Retry.of("myService", config);

Security

Generate Secure Random String

SecureRandom random = new SecureRandom();
byte[] bytes = new byte[32];
random.nextBytes(bytes);
String token = Base64.getUrlEncoder().withoutPadding().encodeToString(bytes);

BCrypt Password Hashing

String hashed = BCrypt.hashpw(password, BCrypt.gensalt(12));
boolean matches = BCrypt.checkpw(password, hashed);