İkinci Seviye Cache — Hangi Cache, Hangi Soruya Cevap Verir?

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dependencies {
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    implementation("org.springframework.boot:spring-boot-starter-data-jpa")
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    implementation("org.hibernate.orm:hibernate-jcache")
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    implementation("org.ehcache:ehcache:3.10.8:jakarta")
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}

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spring:
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  jpa:
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    properties:
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      jakarta.persistence.sharedCache.mode: ENABLE_SELECTIVE   # only entities marked @Cache
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      hibernate:
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        cache:
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          use_second_level_cache: true
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          use_query_cache: true
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          region.factory_class: jcache
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        javax.cache:
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          provider: org.ehcache.jsr107.EhcacheCachingProvider
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          uri: classpath:ehcache.xml
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        generate_statistics: true        # hit/miss counts; keep it on in staging

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<config xmlns="http://www.ehcache.org/v3">
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  <cache alias="com.bank.reference.Currency">
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    <heap unit="entries">500</heap>               <!-- read-only data: no expiry needed -->
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  </cache>
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  <cache alias="com.bank.reference.ProductGroup">
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    <expiry><ttl unit="minutes">30</ttl></expiry>
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    <heap unit="entries">5000</heap>
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  </cache>
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  <cache alias="com.bank.reference.ProductGroup.children">
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    <expiry><ttl unit="minutes">30</ttl></expiry>
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    <heap unit="entries">5000</heap>
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  </cache>
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  <cache alias="default-query-results-region">
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    <expiry><ttl unit="minutes">5</ttl></expiry>
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    <heap unit="entries">1000</heap>
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  </cache>
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  <!-- Must outlive every query result it guards: no expiry. -->
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  <cache alias="default-update-timestamps-region">
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    <heap unit="entries">1000</heap>
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  </cache>
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</config>

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// Two entities in one listing for brevity; in the project each has its own file.
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@Entity
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@Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
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class Currency {                                // ISO 4217 list: loaded once, never edited here
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    @Id private String code;                    // "TRY", "EUR", …
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    private String name;
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    private int minorUnits;                     // 2 for TRY, 0 for JPY
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}
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@Entity
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@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
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class ProductGroup {                            // "Mevduat" > "Vadeli", "Vadesiz"; edited only in this app's product admin
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    @Id @GeneratedValue(strategy = GenerationType.SEQUENCE)
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    private Long id;
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    private String name;
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    @ManyToOne(fetch = FetchType.LAZY)
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    private ProductGroup parent;
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    // The collection is a separate region and holds ids only:
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    // the ProductGroup entities themselves must be cached too.
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    @OneToMany(mappedBy = "parent")
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    @Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
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    private List<ProductGroup> children = new ArrayList<>();
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    protected ProductGroup() {}
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    ProductGroup(String name) {
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        this.name = name;
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    }
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    Long getId() { return id; }
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}

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interface ProductGroupRepository extends JpaRepository<ProductGroup, Long> {
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    // Product menu: every screen of the app asks for it; the tree changes a few times a year.
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    // The query cache stores the ids; the entities come from the ProductGroup region.
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    @QueryHints(@QueryHint(name = "org.hibernate.cacheable", value = "true"))
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    @Query("select c from ProductGroup c where c.parent is null order by c.name")
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    List<ProductGroup> findRoots();
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}

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@SpringBootTest
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class ProductGroupCacheTest {
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    @Autowired ProductGroupRepository productGroups;
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    @Autowired EntityManagerFactory emf;
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    @Autowired TransactionTemplate tx;
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    @Test
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    void secondRequestIsServedFromL2() {
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        Long id = tx.execute(status -> productGroups.save(new ProductGroup("Mevduat")).getId());
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        Statistics stats = emf.unwrap(SessionFactory.class).getStatistics();
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        stats.clear();
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        tx.executeWithoutResult(status -> productGroups.findById(id).orElseThrow());   // new persistence context
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        tx.executeWithoutResult(status -> productGroups.findById(id).orElseThrow());   // and another
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        assertThat(stats.getSecondLevelCacheHitCount()).isGreaterThanOrEqualTo(1);
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        assertThat(stats.getEntityLoadCount()).isZero();   // no SELECT: put on save, hits on both reads
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    }
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}