Hibernate 在使用查询缓存时执行 N+1 次选择而不是 1 次查询
Hibernate performs N+1 selects instead of 1 query when using the Query Cache
我被一个问题困住了，我真的很迷茫，不知道该怎么办。我使用查询缓存+二级缓存，我想把结果适当缓存10秒。所以这是我的
ehcache.xml:
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
<diskStore path="java.io.tmpdir"/>
<cache name = "TestEntity"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="11"
memoryStoreEvictionPolicy="LRU">
</cache>
<cache name="org.hibernate.cache.internal.StandardQueryCache"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="10"
memoryStoreEvictionPolicy="LRU">
</cache>
<defaultCache
maxElementsInMemory="10000"
eternal="false"
timeToLiveSeconds="120"
maxElementsOnDisk="100"
diskExpiryThreadIntervalSeconds="120"
memoryStoreEvictionPolicy="LRU">
<persistence strategy="localTempSwap"/>
</defaultCache>
</ehcache>
首先，我使用 insert() 方法填充我的数据库。
然后，我第一次调用我的 select() 方法来获取数据。一切正常——查询和实体被缓存，如果我在 2 秒后调用 select() 方法，我将在不向数据库发出任何请求的情况下获取数据。
然后我等待 12 秒（以便缓存完全过期），调用 select() 并在调用 select( ) 再一次。这就是我得到 n+1 selects:
的地方
2019-02-13 18:52:17,101 [DEBUG]
org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92)
select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_
from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,107
[DEBUG]
org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92)
select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_
from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,108
[DEBUG]
org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92)
select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_
from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,108
[DEBUG]
org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92)
select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_
from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,109
[DEBUG]
org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92)
select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_
from test testentity0_ where testentity0_.id=?
我知道发出这些请求是因为查询缓存仅缓存 ID，而且二级缓存中似乎缺少这些 ID 的实体。但他们为什么不见了？当我启用完整日志记录时，我看到在第三次调用 select() 之后，有像
这样的日志条目
Adding entity to second-level cache: [TestEntity#1]
所以如果实体被添加到二级缓存并且它们应该只在 11 秒后过期，为什么它们在 2 秒后就丢失了？
我的一部分pom.xml:
<dependencies>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.4.194</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.2.7.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-ehcache</artifactId>
<version>5.2.7.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-c3p0</artifactId>
<version>5.2.7.Final</version>
</dependency>
</dependencies>
persistence.xml:
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="main">
<class>TestEntity</class>
<exclude-unlisted-classes>true</exclude-unlisted-classes>
<properties>
<property name="hibernate.hbm2ddl.auto" value="create-drop"/>
<property name="hibernate.use_sql_comments" value="true"/>
<property name="hibernate.cache.use_second_level_cache" value="true"/>
<property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.EhCacheRegionFactory"/>
<property name="hibernate.cache.use_query_cache" value="true"/>
<property name="net.sf.ehcache.configurationResourceName" value="ehcache.xml"/>
</properties>
</persistence-unit>
</persistence>
TestEntity.java:
import org.hibernate.annotations.CacheConcurrencyStrategy;
import javax.persistence.*;
/**
* User: Kirill Smirnov (k.smirnov@sirena2000.ru)
* Date: 18.12.18
* Time: 19:20
*/
@Entity
@Table(name = "test")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class TestEntity {
@Id
@GeneratedValue(generator = "test_seq")
@SequenceGenerator(name = "test_seq", sequenceName="TEST_SEQ")
@Column(name = "id")
private int id;
@Column(name = "value", nullable = false)
private String value;
public TestEntity() {
}
public TestEntity(String value) {
this.value = value;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
Main.java:
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.TypedQuery;
import java.util.Properties;
/**
* User: Kirill Smirnov (k.smirnov@sirena2000.ru)
* Date: 14.11.14
* Time: 15:55
*/
public class Main {
public static void main(String[] args) throws Exception {
Properties entityManagerFactoryProperties = new Properties();
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.driver", "org.h2.Driver");
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.url", "jdbc:h2:mem:");
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.user", "sa");
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.password", "");
entityManagerFactoryProperties.setProperty("hibernate.c3p0.min_size", "" + 1);
entityManagerFactoryProperties.setProperty("hibernate.c3p0.max_size", "" + 1);
entityManagerFactoryProperties.setProperty("hibernate.c3p0.timeout", "" + 5000);
EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("main", entityManagerFactoryProperties);
insert(entityManagerFactory);
select(entityManagerFactory);
Thread.sleep(2000);
select(entityManagerFactory);
Thread.sleep(12000);
select(entityManagerFactory);
Thread.sleep(2000);
select(entityManagerFactory);
entityManagerFactory.close();
}
private static void insert(EntityManagerFactory entityManagerFactory) {
EntityManager entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
try {
entityManager.persist(new TestEntity("1"));
entityManager.persist(new TestEntity("2"));
entityManager.persist(new TestEntity("3"));
entityManager.persist(new TestEntity("4"));
entityManager.persist(new TestEntity("5"));
entityManager.getTransaction().commit();
} catch (Exception e) {
entityManager.getTransaction().rollback();
throw e;
} finally {
entityManager.close();
}
}
private static void select(EntityManagerFactory entityManagerFactory) {
EntityManager entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
try {
String queryText = "FROM TestEntity";
TypedQuery<TestEntity> query = entityManager.createQuery(queryText, TestEntity.class).setHint("org.hibernate.cacheable", true);
query.getResultList();
entityManager.getTransaction().commit();
} catch (Exception e) {
entityManager.getTransaction().rollback();
throw e;
} finally {
entityManager.close();
}
}
}
P.S。我猜问题的原因是 Hibernate 中的一个错误。如果我从 5.2 升级到 5.4，问题就会消失。但是我接受 Vlad 的回答，因为它包含一般有用的信息。
这就是臭名昭著的N+1 Query Cache issue。
您必须确保实体缓存区域的 TTL（生存时间）高于查询缓存或集合缓存的 TTL。
否则，Hibernate 将在查询缓存或集合缓存中查找实体标识符，并假定实体已存储在实体缓存区域中。但是如果在实体缓存中找不到实体，那么只能从数据库中获取它们，因此会触发 N+1 查询问题。
现在，回到您的设置。这是您为实体缓存区域设置的内容：
<cache name = "TestEntity"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="10"
memoryStoreEvictionPolicy="LRU">
</cache>
请注意 timeToLiveSeconds 仅设置为 10 秒。
QueryCache 是这样设置的：
<cache name="org.hibernate.cache.internal.StandardQueryCache"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="10"
memoryStoreEvictionPolicy="LRU">
</cache>
因此 timeToLiveSeconds 也设置为 10 秒，并确保实体查询缓存未设置为比查询缓存和关联的集合缓存更早过期。
接下来，将 timeToLiveSeconds 的 TestEntity 提高到 60 或 120 秒。或者使其成为 eternal = true 并禁用 TTL 因为实体正在使用 CacheConcurrencyStartegy.READ_ONLY.
<cache name = "TestEntity"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="60"
memoryStoreEvictionPolicy="LRU">
</cache>
我被一个问题困住了，我真的很迷茫，不知道该怎么办。我使用查询缓存+二级缓存，我想把结果适当缓存10秒。所以这是我的
ehcache.xml:
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
<diskStore path="java.io.tmpdir"/>
<cache name = "TestEntity"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="11"
memoryStoreEvictionPolicy="LRU">
</cache>
<cache name="org.hibernate.cache.internal.StandardQueryCache"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="10"
memoryStoreEvictionPolicy="LRU">
</cache>
<defaultCache
maxElementsInMemory="10000"
eternal="false"
timeToLiveSeconds="120"
maxElementsOnDisk="100"
diskExpiryThreadIntervalSeconds="120"
memoryStoreEvictionPolicy="LRU">
<persistence strategy="localTempSwap"/>
</defaultCache>
</ehcache>
首先，我使用 insert() 方法填充我的数据库。 然后，我第一次调用我的 select() 方法来获取数据。一切正常——查询和实体被缓存，如果我在 2 秒后调用 select() 方法，我将在不向数据库发出任何请求的情况下获取数据。 然后我等待 12 秒（以便缓存完全过期），调用 select() 并在调用 select( ) 再一次。这就是我得到 n+1 selects:
的地方2019-02-13 18:52:17,101 [DEBUG] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92) select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_ from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,107 [DEBUG] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92) select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_ from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,108 [DEBUG] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92) select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_ from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,108 [DEBUG] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92) select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_ from test testentity0_ where testentity0_.id=? 2019-02-13 18:52:17,109 [DEBUG] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:92) select testentity0_.id as id1_0_0_, testentity0_.value as value2_0_0_ from test testentity0_ where testentity0_.id=?
我知道发出这些请求是因为查询缓存仅缓存 ID，而且二级缓存中似乎缺少这些 ID 的实体。但他们为什么不见了？当我启用完整日志记录时，我看到在第三次调用 select() 之后，有像
这样的日志条目Adding entity to second-level cache: [TestEntity#1]
所以如果实体被添加到二级缓存并且它们应该只在 11 秒后过期，为什么它们在 2 秒后就丢失了？
我的一部分pom.xml:
<dependencies>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.4.194</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.2.7.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-ehcache</artifactId>
<version>5.2.7.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-c3p0</artifactId>
<version>5.2.7.Final</version>
</dependency>
</dependencies>
persistence.xml:
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="main">
<class>TestEntity</class>
<exclude-unlisted-classes>true</exclude-unlisted-classes>
<properties>
<property name="hibernate.hbm2ddl.auto" value="create-drop"/>
<property name="hibernate.use_sql_comments" value="true"/>
<property name="hibernate.cache.use_second_level_cache" value="true"/>
<property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.EhCacheRegionFactory"/>
<property name="hibernate.cache.use_query_cache" value="true"/>
<property name="net.sf.ehcache.configurationResourceName" value="ehcache.xml"/>
</properties>
</persistence-unit>
</persistence>
TestEntity.java:
import org.hibernate.annotations.CacheConcurrencyStrategy;
import javax.persistence.*;
/**
* User: Kirill Smirnov (k.smirnov@sirena2000.ru)
* Date: 18.12.18
* Time: 19:20
*/
@Entity
@Table(name = "test")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class TestEntity {
@Id
@GeneratedValue(generator = "test_seq")
@SequenceGenerator(name = "test_seq", sequenceName="TEST_SEQ")
@Column(name = "id")
private int id;
@Column(name = "value", nullable = false)
private String value;
public TestEntity() {
}
public TestEntity(String value) {
this.value = value;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
Main.java:
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.TypedQuery;
import java.util.Properties;
/**
* User: Kirill Smirnov (k.smirnov@sirena2000.ru)
* Date: 14.11.14
* Time: 15:55
*/
public class Main {
public static void main(String[] args) throws Exception {
Properties entityManagerFactoryProperties = new Properties();
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.driver", "org.h2.Driver");
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.url", "jdbc:h2:mem:");
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.user", "sa");
entityManagerFactoryProperties.setProperty("javax.persistence.jdbc.password", "");
entityManagerFactoryProperties.setProperty("hibernate.c3p0.min_size", "" + 1);
entityManagerFactoryProperties.setProperty("hibernate.c3p0.max_size", "" + 1);
entityManagerFactoryProperties.setProperty("hibernate.c3p0.timeout", "" + 5000);
EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("main", entityManagerFactoryProperties);
insert(entityManagerFactory);
select(entityManagerFactory);
Thread.sleep(2000);
select(entityManagerFactory);
Thread.sleep(12000);
select(entityManagerFactory);
Thread.sleep(2000);
select(entityManagerFactory);
entityManagerFactory.close();
}
private static void insert(EntityManagerFactory entityManagerFactory) {
EntityManager entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
try {
entityManager.persist(new TestEntity("1"));
entityManager.persist(new TestEntity("2"));
entityManager.persist(new TestEntity("3"));
entityManager.persist(new TestEntity("4"));
entityManager.persist(new TestEntity("5"));
entityManager.getTransaction().commit();
} catch (Exception e) {
entityManager.getTransaction().rollback();
throw e;
} finally {
entityManager.close();
}
}
private static void select(EntityManagerFactory entityManagerFactory) {
EntityManager entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
try {
String queryText = "FROM TestEntity";
TypedQuery<TestEntity> query = entityManager.createQuery(queryText, TestEntity.class).setHint("org.hibernate.cacheable", true);
query.getResultList();
entityManager.getTransaction().commit();
} catch (Exception e) {
entityManager.getTransaction().rollback();
throw e;
} finally {
entityManager.close();
}
}
}
P.S。我猜问题的原因是 Hibernate 中的一个错误。如果我从 5.2 升级到 5.4，问题就会消失。但是我接受 Vlad 的回答，因为它包含一般有用的信息。
这就是臭名昭著的N+1 Query Cache issue。
您必须确保实体缓存区域的 TTL（生存时间）高于查询缓存或集合缓存的 TTL。
否则，Hibernate 将在查询缓存或集合缓存中查找实体标识符，并假定实体已存储在实体缓存区域中。但是如果在实体缓存中找不到实体，那么只能从数据库中获取它们，因此会触发 N+1 查询问题。
现在，回到您的设置。这是您为实体缓存区域设置的内容：
<cache name = "TestEntity"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="10"
memoryStoreEvictionPolicy="LRU">
</cache>
请注意 timeToLiveSeconds 仅设置为 10 秒。
QueryCache 是这样设置的：
<cache name="org.hibernate.cache.internal.StandardQueryCache"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="10"
memoryStoreEvictionPolicy="LRU">
</cache>
因此 timeToLiveSeconds 也设置为 10 秒，并确保实体查询缓存未设置为比查询缓存和关联的集合缓存更早过期。
接下来，将 timeToLiveSeconds 的 TestEntity 提高到 60 或 120 秒。或者使其成为 eternal = true 并禁用 TTL 因为实体正在使用 CacheConcurrencyStartegy.READ_ONLY.
<cache name = "TestEntity"
maxElementsInMemory="100"
eternal="false"
timeToLiveSeconds="60"
memoryStoreEvictionPolicy="LRU">
</cache>