Hibernate Performance Tuning @JUG Thüringen
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The document discusses various techniques for improving performance when persisting data with Hibernate, including recognizing common causes of slow performance like lazy fetching creating multiple queries; solutions like using fetch joins, named entity graphs, and caching at the session/query level; and recommendations to benchmark changes and only cache seldom-updated data.
![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
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![QueryCache • Stores query results for a query and its parameters
• [„FROM AuthorWHERE id=?“, 1] [1]
• Stores only entity references or scalars
• Always use together with 2nd Level Cache
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Hibernate Performance Tuning @JUG Thüringen
- 2. www.thoughts-on-java.org CDI 2.0 Expert Group Member Independent author and trainer www.thoughts-on-java.org @thjanssen123 /c/ThoughtsOnJava /ThoughtsOnJava HibernateTips More than 70 solutions to common Hibernate problems www.hibernate-tips.com ThorbenJanssen
- 5. Performance • Recognize performance problems as early as possible • Typical causes for performance problems • Solving performance problems www.thoughts-on-java.org
- 7. HibernateStatistics • Activate via system property • hibernate.generate_statistics = true • Configure logging • org.hibernate.stat = DEBUG www.thoughts-on-java.org
- 9. Typical causes for performance problems www.thoughts-on-java.org
- 10. TypicalCauses • Slow SELECT statements • Wrong FetchType • Load same data multiple times • Delete or edit records one by one • Put logic into the application instead of the database/query www.thoughts-on-java.org
- 12. 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 www.thoughts-on-java.org
- 13. 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 www.thoughts-on-java.org
- 16. FetchType • Defines when the relationship will be fetched • Static definition in entity mapping www.thoughts-on-java.org @ManyToMany(mappedBy="authors", fetch = FetchType.EAGER) private Set<Book> books;
- 17. FetchType • Lazy • Relationship gets loaded at first access • Default for to-many relationships • Eager • Loads relationships immediately • Default for to-one relationships www.thoughts-on-java.org
- 18. Recommendation s• 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 www.thoughts-on-java.org
- 20. N+1Select? • Most common cause for performance problems • Lazy fetching of related entities creates too many queries www.thoughts-on-java.org 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.”)); }
- 21. Queryspecificfetching • Fetch all required entities with one query • Fetch Joins • @NamedEntityGraph • EntityGraph www.thoughts-on-java.org
- 23. FetchJoin • Use JOIN FETCH instead of JOIN in JPQL query www.thoughts-on-java.org List<Author> authors = this.em.createQuery( "SELECT DISTINCT a FROM Author a JOIN FETCH a.books b", Author.class).getResultList();
- 25. FetchJoin • Advantages • Relationships gets loaded in same query • Disadvantages • Requires a special query for each use case • Creates cartesian product www.thoughts-on-java.org
- 27. NamedEntityGrap h• Introduced in JPA 2.1 • Declaratively defines a graph of entities which will be loaded • Graph is query independent www.thoughts-on-java.org
- 29. NamedEntityGrap h• 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 www.thoughts-on-java.org
- 30. NamedEntityGrap h• Advantages • Query specific EAGER loading • Definition of the graph is independent of the query • Disadvantages • Creates cartesian product www.thoughts-on-java.org
- 32. EntityGraph • Introduced in JPA 2.1 • Dynamic version of @NamedEntityGraph • Definition via Java API • Graph is query independent www.thoughts-on-java.org
- 33. EntityGraph • Define and use EntityGraph www.thoughts-on-java.org 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);
- 34. EntityGraph • Advantages • Query specific EAGER loading • Definition of the graph is independent of the query • Dynamic creation at runtime • Disadvantages • Creates cartesian product www.thoughts-on-java.org
- 38. 1stLevelCache • Activated by default • Linked to the Hibernate session • Stores all entities that were used within a session • Transparent usage www.thoughts-on-java.org
- 40. 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 www.thoughts-on-java.org
- 41. 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 www.thoughts-on-java.org
- 43. 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 www.thoughts-on-java.org
- 45. 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")) www.thoughts-on-java.org
- 46. QueryCache • Stores query results for a query and its parameters • [„FROM AuthorWHERE id=?“, 1] [1] • Stores only entity references or scalars • Always use together with 2nd Level Cache www.thoughts-on-java.org
- 48. Recommendation s• 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 www.thoughts-on-java.org
- 49. www.thoughts-on-java.org thoughts-on-java.org @thjanssen123 /c/ThoughtsOnJava /ThoughtsOnJava HibernateTips More than 70 solutions to common Hibernate problems www.hibernate-tips.com Online & Inhouse Training Coaching & Consulting
Editor's Notes
- #2: 1
- #21: The n+1 select issue is the most common cause for JPA related performance issues. It describes the inefficiency that occurs, if the persistence provider needs to perform additional queries to initialize lazy fetched relationships to other entities. Click Like in this code snippet. As you can see, the query in the first line selects all authors from the database and we then iterate through all of them and print out their names and the number of books they have written. This simple code snippet creates n+1 queries, if FetchType.LAZY is used for the relationship between the Author and the Book entities. In that case, Hibernate or any other JPA persistence provider, needs to perform an additional query in each iteration to get the Books of that Author from the database. So in the end, Hibernate performs n+1 queries. 1 to get n Authors from the database and additional n queries to initialize the Books relationship.