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Performance Tuning@Sander_Makbranchandbound.net

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Hibernate sucks! ... because it’s slow

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Hibernate sucks! ... because it’s slow ‘The problem is sort of cultural [..] developers use Hibernate because they are uncomfortable with SQL and with RDBMSes. You should be very comfortable with SQL and JDBC before you start using Hibernate - Hibernate builds on JDBC, it doesn’t replace it. That is the cost of extra abstraction [..] save yourself effort, pay attention to the database at all stages of development.’ - Gavin King (creator)

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‘Most of the performance problems we have comeup against have been solved not by codeoptimizations, but by adding new functionality.’ - Gavin King (creator)

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‘You cant communicate complexity,only an awareness of it.’ - Alan J. Perlis (1st Turing Award winner)

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Outline Optimization Lazy loading Examples ‘from the trenches’ Search queries Large collections Batching Odds & Ends

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Optimization

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Optimization is hard Performance blame Framework vs. You When to optimize? Preserve correctness at all times Unit tests ok, but not enough Automated integration tests

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Optimization is hard Performance blame Framework vs. You When to optimize? Preserve correctness at all times Unit tests ok, but not enough Automated integration tests Premature optimization is the root of all evil - Donald Knuth

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Optimization guidelinesMeasurement Ensure stable, production-like environment Measure time and space Time: isolate timings in different layers Space: more heap -> longer GC -> slower Try to measure in RDBMS as well IO statistics (hot cache or disk thrashing?) Query plans Make many measurements -> automation

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Optimization guidelinesPractical Profiler on DAO/Session.query() methods VisualVM etc. for heap usage many commercial tools also have built-in JDBC profiling Hibernate JMX <property name="hibernate.generate_statistics">true </property> RDBMS monitoring tools

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Analyzing HibernateLog SQL: <property name="show_sql">true</property> <property name="format_sql">true</property>Log4J configuration: org.hibernate.SQL -> DEBUG org.hibernate.type -> TRACE (see bound params)Or use P6Spy/Log4JDBC on JDBC connection

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Analyzing Hibernate 2011-07-28 09:57:12,061 DEBUG org.hibernate.SQL - insert into BASKET_LINE_ALLOC (LAST_UPDATED, QUANTITY, CUSTOMER_REF, NOTES, BRANCH_ID, FUND_ID, TEMPLATE_ID, BASKET_LINE_ALLOC_ID) values (?, ?, ?, ?, ?, ?, ?, ?)Log SQL: 2011-07-28 09:57:12,081 DEBUG org.hibernate.type.TimestampType - binding 2006-07-28 09:57:12 to parameter: 1 2011-07-28 09:57:12,081 DEBUG org.hibernate.type.IntegerType - binding 3 to parameter: 2 <property name="show_sql">true</property> 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.StringType - binding to parameter: 3 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.StringType - binding to parameter: 4 <property name="format_sql">true</property> 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding 511 to parameter: 5 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding 512 to parameter: 6 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding null to parameter: 7 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding 180030 to parameter: 8 Hibernate: INSERT INTO mkyong.stock_transaction (CHANGE, CLOSE, DATE, OPEN, STOCK_ID, VOLUME)Log4J configuration: VALUES (?, ?, ?, ?, ?, ?) 2011-07-28 13:33:07,253 DEBUG FloatType:133 - binding 10.0 to parameter: 1 2011-07-28 13:33:07,253 DEBUG FloatType:133 - binding 1.1 to parameter: 2 2011-07-28 13:33:07,253 DEBUG DateType:133 - binding 30 December 2009 to parameter: 3 org.hibernate.SQL -> DEBUG 2011-07-28 13:33:07,269 DEBUG FloatType:133 - binding 1.2 to parameter: 4 2011-07-28 13:33:07,269 DEBUG IntegerType:133 - binding 11 to parameter: 5 2011-07-28 13:33:07,269 DEBUG LongType:133 - binding 1000000 to parameter: 6 2011-07-28 09:57:12,061 DEBUG org.hibernate.SQL - insert into BASKET_LINE_ALLOC (LAST_UPDATED, QUANTITY, CUSTOMER_REF, NOTES, BRANCH_ID, FUND_ID, TEMPLATE_ID, org.hibernate.type -> TRACE (see bound params) BASKET_LINE_ALLOC_ID) values (?, ?, ?, ?, ?, ?, ?, ?) 2011-07-28 09:57:12,081 DEBUG org.hibernate.type.TimestampType - binding 2006-07-28 09:57:12 to 2011-07-28 09:57:12,081 DEBUG org.hibernate.type.IntegerType - binding 3 to parameter: 2 parameter: 1 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.StringType - binding to parameter: 3 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.StringType - binding to parameter: 4 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding 511 to parameter: 5 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding 512 to parameter: 6 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding null to parameter: 7Or use P6Spy/Log4JDBC on JDBC connection 2011-07-28 09:57:12,082 DEBUG org.hibernate.type.LongType - binding 180030 to parameter: 8 Hibernate: INSERT INTO mkyong.stock_transaction (CHANGE, CLOSE, DATE, OPEN, STOCK_ID, VOLUME) VALUES (?, ?, ?, ?, ?, ?) 2011-07-28 13:33:07,253 DEBUG FloatType:133 - binding 10.0 to parameter: 1 2011-07-28 13:33:07,253 DEBUG FloatType:133 - binding 1.1 to parameter: 2 2011-07-28 13:33:07,253 DEBUG DateType:133 - binding 30 December 2009 to parameter: 3 2011-07-28 13:33:07,269 DEBUG FloatType:133 - binding 1.2 to parameter: 4 2011-07-28 13:33:07,269 DEBUG IntegerType:133 - binding 11 to parameter: 5 2011-07-28 13:33:07,269 DEBUG LongType:133 - binding 1000000 to parameter: 6

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Lazy loading

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Lazy loadingOne entity to rule them all RequestMostly sane defaults: 1..1@OneToOne,@OneToMany, User@ManyToMany: LAZY 1..* *..1@ManyToOne : EAGER(Due to JPA spec.) AuthorizationExtra-lazy: Hibernate *..1specific Global Company 1..* Company

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LazyInitializationException

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Lazy loading N+1 Selects problemSelect list of N users HQL: SELECT u FROM UserAuthorizations necessary: SQL 1 query: SELECT * FROM User N select queries on LEFT JOIN Company c Authorization executed! WHERE u.worksForCompany = c.idSolution: FETCH JOINS @Fetch(FetchMode.JOI N) @FetchProfile (enable per session don’t call .size()

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Lazy loading N+1 Selects problemSelect list of N users HQL: SELECT u FROM UserAuthorizations necessary: SQL N queries: SELECT * FROM Authorization N select queries on WHERE userId = N Authorization executed!Solution: FETCH JOINS @Fetch(FetchMode.JOI N) @FetchProfile (enable per session don’t call .size()

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Lazy loading N+1 Selects problem HQL: SELECT u FROM User OUTERSelect list of N users JOIN FETCH u.authorizationsAuthorizations necessary: SQL 1 query: N select queries on SELECT * FROM User Authorization executed! LEFT JOIN Company c LEFT OUTER JOIN AuthorizationSolution: ON .. WHERE u.worksForCompany = c.id FETCH JOINS @Fetch(FetchMode.JOI N) @FetchProfile (enable per session don’t call .size()

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Lazy loadingSome guidelines Laziness by default = mostly good However, architectural impact: Session lifetime (‘OpenSessionInView’ pattern) Extended Persistence Context Proxy usage (runtime code generation) Eagerness can be forced with HQL/JPAQL/Criteria But eagerness cannot be reverted exception: Session.load()/EntityManager.getReference()

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Search queries

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Search queries Search User Result list 1..* *..1Authorization *..1 Global 1..* Company Company Detail

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Search queriesObvious solution:Too much information!Use summary objects:UserSummary = POJO not attached, only necessary fields (no relations)

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Search queriesObvious solution:Too much information!Use summary objects:UserSummary = POJO not attached, only necessary fields (no relations) Or: drop down to JDBC to fetch id + fields

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Search queriesAlternative:Taking it further:Pagination in queries, not in app. codeExtra count query may be necessary (totals) Ordering necessary for paging!

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Search queries Subtle:Alternative: effect of applying setMaxResults “The or setFirstResult to a query involving fetch joins over collections is undefined”Taking it further: Cause: the emitted join possibly returns several rows per entity. So LIMIT, rownums, TOP cannot be used! Instead Hibernate must fetch all rows WARNING: firstResult/maxResults specified withPagination in queries, not in app. code collection fetch; applying in memory!Extra count query may be necessary (totals) Ordering necessary for paging!

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Analytics & reporting ORM less relevant: no entities, but complex aggregations Simple sum/avg/counts possible over entities Specialized db calls for complex reports: Partitioning/windowing etc. Integrate using native query Or create a database view and map entity

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Large collections

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Large collections Frontend: Request CompanyGroup 1..* Backend: Company CompanyGroup 1..* Meta-dataCompany read-only entity, CompanyInGroupbacked by expensive view *..1 Company

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Large collections Frontend: Request CompanyGroup 1..* Backend: Company CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Large collections Frontend: Request CompanyGroup 1..* Backend: Company CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Large collections Opening large groups sluggish Improved performance: Fetches many uninitialized collections in 1 query Also possible on entity: Request CompanyGroup 1..* Company

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Large collections Opening large groups sluggish Improved performance: Fetches many uninitialized collections in 1 query Also possible on entity: Request CompanyGroup 1..* Company Better solution in hindsight: fetch join

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Large collections Extra lazy collection fetching Efficient: companies.size() -> count query companies.contains() -> select 1 where ... companies.get(n) -> select * where index = n

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Large collections Saving large group slow: >15 sec. Problem: Hibernate inserts row by row Query creation overhead, network latency Solution: <property name="hibernate.jdbc.batch_size">100 </property> Enables JDBC batched statements Caution: global property Request CompanyGroup Also: <property name="hibernate.order_inserts">true 1..* </property> Company <property name="hibernate.order_updates">true </property>

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Large collections Frontend: Request CompanyGroup 1..* Backend: Company CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Large collections Backend: CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Large collectionsProcess CreateGroup (Soap) BusinessService Service CreateGroup: ~10 min. for thousands of companies @BatchSize on Company improved demarshalling JDBC batch_size property marginal improvement INFO: INSERT INTO CompanyInGroup VALUES (?,...,?) INFO: SELECT @identity INFO: INSERT INTO CompanyInGroup VALUES (?,...,?) INFO: SELECT @identity .. 1000 times CompanyGroup 1..* Meta-data Insert/select interleaved: due to gen. id CompanyInGroup *..1 Company

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Large collectionsProcess CreateGroup (Soap) BusinessService Service Solution: generate id in app. (not always feasible) Running in ~3 minutes with batched inserts Next problem: heap usage spiking Use StatelessSession ✦ Bypass first-level cache ✦ No automatic dirty checking CompanyGroup ✦ Bypass Hibernate event model and interceptors 1..* Meta-data ✦ No cascading of operations CompanyInGroup ✦ Collections on entities are ignored *..1 Company

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Large collectionsProcess CreateGroup (Soap) BusinessService Service Solution: generate id in app. (not always feasible) Running in ~3 minutes with batched inserts Next problem: heap usage spiking Use StatelessSession CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Large collectionsProcess CreateGroup (Soap) BusinessService Service Now <1 min., everybody happy! CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Large collectionsProcess CreateGroup (Soap) BusinessService Service Now <1 min., everybody happy! Data loss detected! CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Large collectionsProcess CreateGroup (Soap) BusinessService Service Data loss detected! StatelessSession and JDBC batch_size bug HHH-4042: Closed, won’t fix : CompanyGroup 1..* Meta-data CompanyInGroup *..1 Company

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Odds & Ends

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Dirty little secret validated(item) performs read-only queries select currentItem from Catalog where .. Dirty collection after select spendingLimit from User where .. each iteration insert into Item values (?, ?, ?) select currentItem from Catalog where .. select spendingLimit from User where .. Batching fails insert into Item values (?, ?, ?) Flushmode.AUTO Loops always suspect: relational, set-based thinking

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Dirty little secret validated(item) performs read-only queries Dirty collection after each iteration Batching fails Flushmode.AUTO Loops always suspect: relational, set-based thinking

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Query hintsSpeed up read-only service calls:Hibernate Query.setHint():Also: never use 2nd level cache just ‘because we can’

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Query hintsSpeed up read-only service calls:Hibernate Query.setHint():Also: never use 2nd level cache just ‘because we can’ @org.hibernate.annotations.Immutable

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Large updatesNaive approach:Entities are not always necessary:Changes are not reflected in persistence contextWith optimistic concurrency: VERSIONED keyword

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Large updatesNaive approach:Entities are not always necessary:Changes are not reflected in persistence contextWith optimistic concurrency: VERSIONED keyword Consider use of stored procedures

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Cherish your databaseData and schema outlive your applicationGood indexes make a world of differenceStored procedures etc. are not inherently evilDo not let Hibernate dictate your schema Befriend a DBA instead!There are other solutions (there I said it) MyBatis Squeryl (Scala)

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Thanks for listening!@Sander_Mak Join me later today: Elevate your webapps with Scala & Lift! 17:00 Room Cbranchandbound.net