Effiziente Datenpersistierung mit JPA 2.1 und Hibernate

Effiziente Datenpersistierung
mit JPA 2.1 und Hibernate
JavaLand 2016
www.thoughts-on-java.org

ThorbenJanssen
• Independent author and trainer
• Senior developer and architect @ Qualitype GmbH
• CDI 2.0 expert group member
• Twitter: @thjanssen123
• Blog: www.thoughts-on-java.org

Performance

Performance
• Recognize performance problems as early as possible
• Typical causes for performance problems
• Solving performance problems

Hibernate Statistics

HibernateStatistics
• Activate via system property
• hibernate.generate_statistics = true
• Configure logging
• org.hibernate.stat = DEBUG

HibernateStatistics
08:24:10,916 DEBUG
[org.hibernate.stat.internal.ConcurrentStatisticsImpl]
(default task-1) HHH000117: HQL: SELECT a FROM Author
a WHERE a.lastName = :lastName, time: 6ms, rows: 1
Time
spend for
this query Number of
returned
rows

HibernateStatistics 08:08:04,960 INFO
[org.hibernate.engine.internal.StatisticalLoggingSessionEventListe
ner] (default task-2) Session Metrics {
1191522 nanoseconds spent acquiring 4 JDBC connections;
433875 nanoseconds spent releasing 4 JDBC connections;
4404058 nanoseconds spent preparing 6 JDBC statements;
12458725 nanoseconds spent executing 6 JDBC statements;
0 nanoseconds spent executing 0 JDBC batches;
0 nanoseconds spent performing 0 L2C puts;
0 nanoseconds spent performing 0 L2C hits;
0 nanoseconds spent performing 0 L2C misses;
586896 nanoseconds spent executing 1 flushes (flushing a total
of 2 entities and 2 collections);
39434974 nanoseconds spent executing 1 partial-flushes
(flushing a total of 2 entities and 2 collections)
Number of SQL
statements
Cache usage
Time
spend
for SQL
state-
ments

Typical causes for performance
problems

TypicalCauses
• Slow SELECT statements
• Wrong FetchType
• Load same data multiple times

Slow SELECT-statements

SlowSELECTs • In general no „real“ JPA or Hibernate problem
• Check generated SQL
• Check execution plan of the statement
• Check indexes
• Optimize SELECT statement
• Consider to use a native query

NativeQuery • Reasons to use native queries:
• JPQL supports only a subset of SQL
• Database specific features
• Native queries return an Object[] for each row
• Needs to be mapped programmatically or declaratively

ResultSetMapping • Declarative mapping of query results
@SqlResultSetMapping(
name = "myResultMapping ",
entities = {@EntityResult(...), …},
classes = {@ConstructorResult (…), …},
columns = {@ColumnResult(…), …}
)
this.em.createNativeQuery(“Select …", "myResultMapping")

ResultSetMapping
name = "myResultMapping",
entities = {@EntityResult(
entityClass = Author.class,
fields = {
@FieldResult(name = "id", column = „autId"),
…}
),
…},
classes = {@ConstructorResult (…), …},
)

ResultSetMapping
classes = {@ConstructorResult(
targetClass = BookPublisherValue.class,
columns = {
@ColumnResult(name = "title"),
…}
),
…},
)

ResultSetMapping
classes = {@ConstructorResult(...), …},
columns = {@ColumnResult(
name = "bookCount",
type = Long.class),
…},
)

FetchType

FetchType
• Defines when the relationship will be fetched
• Static definition in entity mapping
@ManyToMany(mappedBy="authors", fetch = FetchType.EAGER)
private Set<Book> books;

FetchType • Lazy
• Relationship gets loaded at first access
• Default for to-many relationships
• Eager
• Loads relationships immediately
• Default for to-one relationships

Recommendations • To-many relationships
• Stick to the default mapping (FetchType.LAZY)
• Use eager fetching for specific queries, if required
• To-one relationships
• Check individually
• Default is fine in most of the cases

Query Specific Fetching

N+1Select? • Most common cause for performance problems
• Lazy fetching of related entities creates too many queries
List<Author> authors = this.em.createQuery("SELECT a FROM Author a",
Author.class).getResultList();
for (Author a : authors) {
System.out.println("Author " + a.getFirstName() + " " + a.getLastName()
+ " wrote " + a.getBooks().size() + “ Books.”));
}

Queryspecificfetching
• Fetch all required entities with one query
• Fetch Joins
• @NamedEntityGraph
• EntityGraph

Fetch Join

FetchJoin
• Use JOIN FETCH instead of JOIN in JPQL query
List<Author> authors = this.em.createQuery(
"SELECT DISTINCT a FROM Author a JOIN FETCH a.books b",
Author.class).getResultList();

FetchJoin • Advantages
• Relationships gets loaded in same query
• Disadvantages
• Requires a special query for each use case
• Creates cartesian product

NamedEntityGraph

NamedEntityGraph • Introduced in JPA 2.1
• Declaratively defines a graph of entities which will be loaded
• Graph is query independent

NamedEntityGraph • Define NamedEntityGraph
@NamedEntityGraph(
name = "graph.AuthorBooksReviews",
attributeNodes =
@NamedAttributeNode(value = "books")
)
@NamedEntityGraph(
name = "graph.AuthorBooksReviews",
attributeNodes =
@NamedAttributeNode(value = "books", subgraph = "books"),
subgraphs =
@NamedSubgraph(
name = "books",
attributeNodes = @NamedAttributeNode("reviews")
)
)

NamedEntityGraph • Provide entity graph es hint
EntityGraph graph = this.em.getEntityGraph("graph.AuthorBooks");
this.em.createQuery("SELECT DISTINCT a FROM Author a")
.setHint("javax.persistence.loadgraph", graph);

NamedEntityGraph • Fetch graph
• Eager loading for all elements of the graph
• Lazy loading for all other attributes
• Load graph
• Eager loading for all elements of the graph
• Loads all other attributes with their defined FetchType
• Hibernate always uses a load graph
• HHH-8776

NamedEntityGraph • Advantages
• Query specific EAGER loading
• Definition of the graph is independent of the query
• Disadvantages

EntityGraph

EntityGraph • Introduced in JPA 2.1
• Dynamic version of @NamedEntityGraph
• Definition via Java API
• Graph is query independent

EntityGraph • Define and use EntityGraph
EntityGraph graph = this.em.createEntityGraph(Author.class);
Subgraph<Book> bookSubGraph = graph.addSubgraph(Author_.books);
bookSubGraph.addSubgraph(Book_.reviews);
this.em.createQuery("SELECT DISTINCT a FROM Author a")
.setHint("javax.persistence.loadgraph", graph);

EntityGraph • Advantages
• Query specific EAGER loading
• Definition of the graph is independent of the query
• Dynamic creation at runtime
• Disadvantages

Caching

Query
Cache
Caches
DB
2nd
Level
Cache
1st
Level
Cache
Hibernate
Session
1st
Level
Cache
Hibernate
Session

1st Level Cache

1stLevelCache
• Activated by default
• Linked to the Hibernate session
• Stores all entities that were used within a session
• Transparent usage

2nd Level Cache

2ndLevelCache • Session independent entity store
• Needs to be activated
• persistence.xml or EntityManagerFactory
• Transparent usage
• PersistenceProvider doesn‘t need to provide it
• Not always portable

2ndLevelCache • Shared Cache Mode
• ALL cache all entities
• NONE cache no entities
• ENABLE_SELECTIVE cache needs to be activated for
specific entities
• DISABLE_SELECTIVE cache can be deactivated for specific
entities
• UNSPECIFIED use default settings of the
PersistenceProvider

2ndLevelCache • Cache configuration
• Cache Retrieve Mode
• How to read entities from the cache
• Cache Store Mode
• How to write entities to the cache
• Concurrency Strategy
• How to handle concurrent access

Query Cache

QueryCache • Hibernate specific
• Stores query result session independent
• Needs to be activated (persistence.xml)
• hibernate.cache.use_query_cache = true
• Activate caching for a specific query
• org.hibernate.Query.setCacheable(true)
• @NamedQuery(… hints =
@QueryHint(name="org.hibernate.cacheable", value="true"))

QueryCache • Stores query results for a query and its parameters
• [„FROM Author WHERE id=?“, 1]  [1]
• Stores only entity references or scalars
• Always use together with 2nd Level Cache

Recommendations • Only cache data that is seldom updated
• Always benchmark the application when adding or changing
caching
• Use Query Cache together with 2nd Level Cache
• Configuration has to fit to each other

Slides & Cheat Sheet

Get this presentation and a handy cheat sheet:
http://www.thoughts-on-java.org/javaland2016/
Follow me on twitter:
@thjanssen123

Resources

Resources • JSR 338: JavaTM Persistence API, Version 2.1
http://download.oracle.com/otndocs/jcp/persistence-
2_1-fr-eval-spec/index.html
• Hibernate Reference Documentation
http://docs.jboss.org/hibernate/orm/4.3/manual/en-
US/html/
• Hibernate Developer Guide
http://docs.jboss.org/hibernate/orm/4.3/devguide/en-
US/html/
• Hibernate ORM: Tips, Tricks and Performance Techniques
by Brett Meyer
http://de.slideshare.net/brmeyer/hibernate-orm-
performance-31550150

Resources • Java Persistence with Hibernate Second Edition by Christian
Bauer, Gaving King, Gary Gregory
• Java Platform, Enterprise Edition: The Java EE Tutorial
https://docs.oracle.com/javaee/7/tutorial/index.html
• Hibernate: Truly Understanding the Second-Level and
Query Caches
http://www.javalobby.org/java/forums/t48846.html

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