2차 캐시 — 영속성 컨텍스트 밖에서도 캐시할 수 있을까

트랜잭션 A                    트랜잭션 B
┌─────────────────────┐     ┌─────────────────────┐
│  영속성 컨텍스트 (1차 캐시) │     │  영속성 컨텍스트 (1차 캐시) │
│  Member(id=1)        │     │  (비어있음)            │
└─────────────────────┘     └─────────────────────┘
         ↓                            ↓
      DB 1번 조회                    DB 1번 조회 (또!)

트랜잭션 A     트랜잭션 B     트랜잭션 C
    ↓              ↓              ↓
┌──────────────────────────────────────┐
│          2차 캐시 (공유)               │
│  Member(id=1) → {name:"심", age:25}   │
└──────────────────────────────────────┘
                  ↓
            DB 1번만 조회

// build.gradle
implementation 'org.hibernate.orm:hibernate-jcache'
implementation 'org.ehcache:ehcache:3.10.8'

# application.yml
spring:
  jpa:
    properties:
      hibernate:
        cache:
          use_second_level_cache: true
          region.factory_class: jcache
        javax:
          cache:
            provider: org.ehcache.jsr107.EhcacheCachingProvider

@Entity
@Cacheable               // JPA 표준 어노테이션
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)  // Hibernate 전용
public class Category {

    @Id @GeneratedValue
    private Long id;
    private String name;
    private String description;
}

@Entity
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Team {

    @OneToMany(mappedBy = "team")
    @Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
    private List<Member> members;
}

spring:
  jpa:
    properties:
      hibernate:
        cache:
          use_query_cache: true

@QueryHints(@QueryHint(name = "org.hibernate.cacheable", value = "true"))
List<Member> findByAge(int age);

@Configuration
@EnableCaching
public class CacheConfig {
}

@Cacheable(value = "categories", key = "#id")
public CategoryDto getCategory(Long id) {
    Category category = categoryRepository.findById(id).orElseThrow();
    return CategoryDto.from(category);
}

@CachePut(value = "categories", key = "#id")
public CategoryDto updateCategory(Long id, UpdateRequest request) {
    Category category = categoryRepository.findById(id).orElseThrow();
    category.update(request);
    return CategoryDto.from(category);
}

@CacheEvict(value = "categories", key = "#id")
public void deleteCategory(Long id) {
    categoryRepository.deleteById(id);
}

implementation 'com.github.ben-manes.caffeine:caffeine'
implementation 'org.springframework.boot:spring-boot-starter-cache'

spring:
  cache:
    type: caffeine
    caffeine:
      spec: maximumSize=500,expireAfterWrite=10m

@Configuration
@EnableCaching
public class CacheConfig {

    @Bean
    public CacheManager cacheManager() {
        CaffeineCacheManager manager = new CaffeineCacheManager();
        manager.registerCustomCache("categories",
            Caffeine.newBuilder()
                .maximumSize(100)
                .expireAfterWrite(Duration.ofMinutes(30))
                .build());
        manager.registerCustomCache("members",
            Caffeine.newBuilder()
                .maximumSize(1000)
                .expireAfterWrite(Duration.ofMinutes(5))
                .build());
        return manager;
    }
}