Performance Anti-Patterns in Hibernate Patrycja Wegrzynowicz CTO Yonita, Inc.Tuesday, November 22, 2011
About Me   • 10+ years of professional experience   • PhD in Computer Science         –Patterns and anti-patterns, static ...
Agenda   • 4 puzzles         –Short program with curious behavior         –Question to you (multiple choice)         –Myst...
Disclaimer                             I do think Hibernate is a great tool!                                              ...
5Tuesday, November 22, 2011
5Tuesday, November 22, 2011
5Tuesday, November 22, 2011
Puzzle #1                                 Less Is MoreTuesday, November 22, 2011
Who knows CaveatEmptor app?                                                           7Tuesday, November 22, 2011
Who’s read Java Persistence                                   with Hibernate?                                             ...
CaveatEmptor   • Demo application from     ‘Java Persistence with     Hibernate’   • Simple auction system                ...
I’m Gonna Win This Auction!   public class PlaceBidAction implements Action {      // invoked in a new transaction      pu...
What’s the Problem?                                                              (a) None (code is correct)               ...
What’s the Problem?   (a) None (the code is correct)   (b) Transaction/Lock management   (c) Exception thrown   (d) None o...
Another Look   public class PlaceBidAction implements Action {       // invoked in a new transaction       public String e...
2 Users and Item with 2 Bids             Thread A (new amount 100)   Thread B (new amount 30)                   (1)   // b...
2 Users and Item with 2 Bids             Thread A (new amount 100)        Thread B (new amount 30)                   (1)  ...
2 Users and Item with 2 Bids             Thread A (new amount 100)         Thread B (new amount 30)                   (1) ...
2 Users and Item with 2 Bids             Thread A (new amount 100)         Thread B (new amount 30)                   (1) ...
How To Fix It?   public class PlaceBidAction implements Action {      // invoked in a new transaction      public String e...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
How To Fix It?                                                                          version and                       ...
Lessons Learned   • Nobody’s perfect ;-)   • ACID is only a theory         –Simple transaction interceptor/annotation ofte...
Performance Lessons   • Object model   • Usage patterns         –Concurrent users         –Data volume   • Transaction and...
Puzzle #2                                Heads of HydraTuesday, November 22, 2011
Heads of Hydra   @Entity   public class Hydra {      private Long id;      private List<Head> heads = new ArrayList<Head>(...
How Many Queries in 2nd Tx?                                                           (a) 1 select                        ...
How Many Queries in 2nd Tx?   (a) 1 select   (b) 2 selects   (c) 1+3 selects   (d) 2 selects, 1 delete, 3 inserts   (e) No...
Another Look   @Entity   public class Hydra {      private Long id;      private List<Head> heads = new ArrayList<Head>();...
How To Fix It?  @Entity  public class Hydra {     @Id @GeneratedValue     private Long id;     @OneToMany(cascade=CascadeT...
Lessons Learned   • Expect unexpected ;-)   • Prefer field access mappings   • And...                                    2...
Anti-Pattern #2                             Lost Collection Proxy on Owning SideTuesday, November 22, 2011
Lost Collection Proxy   • Description         –On the owning side of an association, we assign a new          collection o...
Lost Collection Proxy - Example   @Entity   public class Hydra {      @Id @GeneratedValue      private Long id;      @OneT...
Lost Collection Proxy - Solution   • Operate on collection objects returned by     hibernate         –In most cases it’s a...
Puzzle #3                             Fashionable DeveloperTuesday, November 22, 2011
Fashionable Developer   @Entity   public class Developer {      @Id @GeneratedValue      private Long id;      private Str...
How Many Queries in 2nd Tx?   @Entity   public class Developer {                                (a) 2 select      @Id @Gen...
How Many Queries in 2nd Tx?   (a) 2 selects   (b) 4 selects   (c) 4 selects, 1 update   (d) 4 selects, 4 inserts   (e) Non...
Fashionable Developer   @Entity   public class Developer {      @Id @GeneratedValue      private Long id;      private Str...
Anti-Pattern #3                                   Temporary ChangesTuesday, November 22, 2011
Temporary Changes   • Description         –We change the persistent data of an object temporarily to          test some fe...
Puzzle #4                                 Plant a TreeTuesday, November 22, 2011
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany      Collect...
How Many Queries in 2nd Tx?   @Entity                                              (a) 1 select, 2 inserts   public class ...
How Many Queries in 2nd Tx?   (a) 1 select, 2 inserts   (b) 2 selects, 2 inserts   (c) 2 selects, 1 delete, 10.000+2 inser...
Plant a Tree - Revisited   @Entity   public class Orchard {      @Id @GeneratedValue      private Long id;      @OneToMany...
Plant a Tree - Revisited   @Entity   public class Orchard {                               STILL BAG SEMANTIC!      @Id @Ge...
Plant a Tree - Revisited   @Entity   public class Orchard {                               STILL BAG SEMANTIC!      @Id @Ge...
OneToMany Mapping                         Seman&c                    Java	  Type               Annota&on                  ...
OneToMany Mapping                                            add	                           remove	                      u...
OneToMany Mapping                                            add	                           remove	                      u...
OneToMany Mapping                                            add	                           remove	                      u...
Anti-Pattern #4                             Inadequate Collection Type (Owning Side)Tuesday, November 22, 2011
Inadequate Collection Mapping (Owning Side)   • Description         –Chosen an inadequate collection mapping on the       ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany      Set<Tre...
Anti-Pattern #5                                OneToMany as Owning SideTuesday, November 22, 2011
OneToMany as Owning Side   • Description         –OneToMany used as the owning side of a relationship   • Consequences    ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany (mappedBy = ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany (mappedBy = ...
Anti-Pattern #6                             Inadequate Collection Type (Inverse Side)Tuesday, November 22, 2011
Inadequate Collection Type (Inverse Side)   • Description         –Set used as a collection type on the inverse side of a ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany (mappedBy = ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany (mappedBy = ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany (mappedBy = ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany (mappedBy = ...
Plant a Tree   @Entity   public class Forest {      @Id @GeneratedValue      private Long id;      @OneToMany (mappedBy = ...
Anti-Pattern #7                                  One by One ProcessingTuesday, November 22, 2011
Inadequate Collection Type (Inverse Side)   • Description         –Sequential processing of a persistent collection/object...
Conclusions   • Big data cause big problems         –Standard mappings don’t handle large datasets well         –Smart mod...
Contact   • email: patrycja@yonita.com   • twitter: @yonlabs   • www: http://www.yonita.com                               ...
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Performance Anti-Patterns in Hibernatee, by Patrycja Wegrzynowicz

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This talk explains common mistakes or omissions related to mappings of complex structures. The focus is on efficient retrieval of collections and their sub-objects along with fetching strategies and efficient queries. The presented real code examples illustrate how the anti-patterns can decrease performance and how to implement the mappings to speed up execution times.

Published in: Technology, Business

Performance Anti-Patterns in Hibernatee, by Patrycja Wegrzynowicz

  1. 1. Performance Anti-Patterns in Hibernate Patrycja Wegrzynowicz CTO Yonita, Inc.Tuesday, November 22, 2011
  2. 2. About Me • 10+ years of professional experience • PhD in Computer Science –Patterns and anti-patterns, static and dynamic code analysis, language semantics, compiler design • Active author and speaker –JavaOne, Devoxx, JavaZone, Jazoon, OOPSLA, ASE... • CTO of Yonita, Inc. –Bridge the gap between the industry and the academia –Automated defects detection and optimization –Performance, security, concurrency, databases • Twitter @yonlabs 2Tuesday, November 22, 2011
  3. 3. Agenda • 4 puzzles –Short program with curious behavior –Question to you (multiple choice) –Mystery revealed –Lessons learned • 7 performance anti-patterns –Description, consequences, solutions 3Tuesday, November 22, 2011
  4. 4. Disclaimer I do think Hibernate is a great tool! 4Tuesday, November 22, 2011
  5. 5. 5Tuesday, November 22, 2011
  6. 6. 5Tuesday, November 22, 2011
  7. 7. 5Tuesday, November 22, 2011
  8. 8. Puzzle #1 Less Is MoreTuesday, November 22, 2011
  9. 9. Who knows CaveatEmptor app? 7Tuesday, November 22, 2011
  10. 10. Who’s read Java Persistence with Hibernate? 8Tuesday, November 22, 2011
  11. 11. CaveatEmptor • Demo application from ‘Java Persistence with Hibernate’ • Simple auction system 9Tuesday, November 22, 2011
  12. 12. I’m Gonna Win This Auction! public class PlaceBidAction implements Action { // invoked in a new transaction public String execute(Map even) { // ... Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 10Tuesday, November 22, 2011
  13. 13. What’s the Problem? (a) None (code is correct) (b) Transaction/lock mgmt public class PlaceBidAction implements Action { (c) Exception thrown // invoked in a new transaction (d) None of the above public String execute(Map even) { // ... Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 11Tuesday, November 22, 2011
  14. 14. What’s the Problem? (a) None (the code is correct) (b) Transaction/Lock management (c) Exception thrown (d) None of the above The bids can change between calling getMaxBid and locking the item. 12Tuesday, November 22, 2011
  15. 15. Another Look public class PlaceBidAction implements Action { // invoked in a new transaction public String execute(Map even) { // ... Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // here, the bids can be modified by a different transaction // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 13Tuesday, November 22, 2011
  16. 16. 2 Users and Item with 2 Bids Thread A (new amount 100) Thread B (new amount 30) (1) // begin transaction // item with 2 bids: 10,20 Bid curMax = dao.getMaxBid(id); // curMax = 20 14Tuesday, November 22, 2011
  17. 17. 2 Users and Item with 2 Bids Thread A (new amount 100) Thread B (new amount 30) (1) (2) // begin transaction // begin transaction // item with 2 bids: 10,20 // item with 2 bids: 10,20 Bid curMax = dao.getMaxBid(id); Bid curMax = dao.getMaxBid(id); // curMax = 20 // curMax = 20 15Tuesday, November 22, 2011
  18. 18. 2 Users and Item with 2 Bids Thread A (new amount 100) Thread B (new amount 30) (1) (2) // begin transaction // begin transaction // item with 2 bids: 10,20 // item with 2 bids: 10,20 Bid curMax = dao.getMaxBid(id); Bid curMax = dao.getMaxBid(id); // curMax = 20 // curMax = 20 (3) // item with 2 bids: 10,20 // Lock.UPGRADE Item item = dao.findById(id,true); Bid newBid = item.placeBid(..., newAmount, curMax, ...); // commit transaction // item with 3 bids: 10,20,100 Successful bid: 100 16Tuesday, November 22, 2011
  19. 19. 2 Users and Item with 2 Bids Thread A (new amount 100) Thread B (new amount 30) (1) (2) // begin transaction // begin transaction // item with 2 bids: 10,20 // item with 2 bids: 10,20 Bid curMax = dao.getMaxBid(id); Bid curMax = dao.getMaxBid(id); // curMax = 20 // curMax = 20 (3) (4) // item with 2 bids: 10,20 // item with 3 bids: 10,20,100 // Lock.UPGRADE // Lock.UPGRADE Item item = dao.findById(id,true); Item item = dao.findById(id,true); Bid newBid = item.placeBid(..., Bid newBid = item.placeBid(..., newAmount, newAmount, curMax, ...); curMax, ...); // commit transaction // commit transaction // item with 3 bids: 10,20,100 // item with 4 bids: 10,20,100,30 Successful bid: 100 Successful bid: 30 17Tuesday, November 22, 2011
  20. 20. How To Fix It? public class PlaceBidAction implements Action { // invoked in a new transaction public String execute(Map even) { // ... Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  21. 21. How To Fix It? version and optimistic locking public class PlaceBidAction implements Action { // invoked in a new transaction public String execute(Map even) { // ... Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  22. 22. How To Fix It? version and NO optimistic locking public class PlaceBidAction implements Action { // invoked in a new transaction public String execute(Map even) { // ... Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  23. 23. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { // invoked in a new transaction READS public String execute(Map even) { // ... Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  24. 24. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  25. 25. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  26. 26. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE YES Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); // uses load with Lock.UPGRADE Item item = itemDAO.findById(itemId, true); Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  27. 27. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE YES Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); move lock before // uses load with Lock.UPGRADE getMinBid/ Item item = itemDAO.findById(itemId, true); getMaxBid Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  28. 28. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE YES Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); move lock before // uses load with Lock.UPGRADE getMinBid/ YES Item item = itemDAO.findById(itemId, true); getMaxBid Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, currentMinBid); // ... } } 18Tuesday, November 22, 2011
  29. 29. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE YES Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); move lock before // uses load with Lock.UPGRADE getMinBid/ YES Item item = itemDAO.findById(itemId, true); getMaxBid Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, different currentMinBid); object model // ... } } 18Tuesday, November 22, 2011
  30. 30. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE YES Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); move lock before // uses load with Lock.UPGRADE getMinBid/ YES Item item = itemDAO.findById(itemId, true); getMaxBid Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, different YES currentMinBid); object model // ... } } 18Tuesday, November 22, 2011
  31. 31. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE YES Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); move lock before // uses load with Lock.UPGRADE getMinBid/ YES Item item = itemDAO.findById(itemId, true); getMaxBid Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, different YES currentMinBid); object model // ... } } Java synchronized 18Tuesday, November 22, 2011
  32. 32. How To Fix It? version and NO optimistic locking REPEATABLE public class PlaceBidAction implements Action { NO // invoked in a new transaction READS public String execute(Map even) { // ... SERIALIZABLE YES Bid currentMinBid = itemDAO.getMinBid(itemId); Bid currentMaxBid = itemDAO.getMaxBid(itemId); move lock before // uses load with Lock.UPGRADE getMinBid/ YES Item item = itemDAO.findById(itemId, true); getMaxBid Bid newBid = item.placeBid(userDAO.findById(userId, false), newAmount, currentMaxBid, different YES currentMinBid); object model // ... } Java } YES synchronized 18Tuesday, November 22, 2011
  33. 33. Lessons Learned • Nobody’s perfect ;-) • ACID is only a theory –Simple transaction interceptor/annotation often is not enough –Query order does matter –Learn more about locks and transaction isolation levels • Premature optimization is the root of all evil –Performance Anti-Pattern #1 19Tuesday, November 22, 2011
  34. 34. Performance Lessons • Object model • Usage patterns –Concurrent users –Data volume • Transaction and locking management 20Tuesday, November 22, 2011
  35. 35. Puzzle #2 Heads of HydraTuesday, November 22, 2011
  36. 36. Heads of Hydra @Entity public class Hydra { private Long id; private List<Head> heads = new ArrayList<Head>(); @Id @GeneratedValue public Long getId() {...} protected void setId() {...} @OneToMany(cascade=CascadeType.ALL) public List<Head> getHeads() { return Collections.unmodifiableList(heads); } protected void setHeads(List<Head> heads) {...} } // creates and persists the hydra with 3 heads // new EntityManager and new transaction Hydra found = em.find(Hydra.class, hydra.getId()); 22Tuesday, November 22, 2011
  37. 37. How Many Queries in 2nd Tx? (a) 1 select (b) 2 selects @Entity (c) 1+3 selects public class Hydra { private Long id; (d) 2 selects, 1 delete, 3 private List<Head> heads = new ArrayList<Head>(); inserts (e) None of the above @Id @GeneratedValue public Long getId() {...} protected void setId() {...} @OneToMany(cascade=CascadeType.ALL) public List<Head> getHeads() { return Collections.unmodifiableList(heads); } protected void setHeads(List<Head> heads) {...} } // creates and persists the hydra with 3 heads // new EntityManager and new transaction Hydra found = em.find(Hydra.class, hydra.getId()); 23Tuesday, November 22, 2011
  38. 38. How Many Queries in 2nd Tx? (a) 1 select (b) 2 selects (c) 1+3 selects (d) 2 selects, 1 delete, 3 inserts (e) None of the above During commit hibernate checks whether the collection property is dirty (needs to be re- created) by comparing Java identities (object references). 24Tuesday, November 22, 2011
  39. 39. Another Look @Entity public class Hydra { private Long id; private List<Head> heads = new ArrayList<Head>(); @Id @GeneratedValue public Long getId() {...} protected void setId() {...} @OneToMany(cascade=CascadeType.ALL) public List<Head> getHeads() { return Collections.unmodifiableList(heads); } protected void setHeads(List<Head> heads) {...} } // creates and persists hydra with three heads // new EntityManager and new transaction // during find only 1 select (hydra) Hydra found = em.find(Hydra.class, hydra.getId()); // during commit 1 select (heads),1 delete (heads),3 inserts (heads) 25Tuesday, November 22, 2011
  40. 40. How To Fix It? @Entity public class Hydra { @Id @GeneratedValue private Long id; @OneToMany(cascade=CascadeType.ALL) private List<Head> heads = new ArrayList<Head>(); public Long getId() {...} protected void setId() {...} public List<Head> getHeads() { return Collections.unmodifiableList(heads); } protected void setHeads(List<Head> heads) {...} } // creates and persists hydra with three heads // new EntityManager and new transaction Hydra found = em.find(Hydra.class, hydra.getId()); 26Tuesday, November 22, 2011
  41. 41. Lessons Learned • Expect unexpected ;-) • Prefer field access mappings • And... 27Tuesday, November 22, 2011
  42. 42. Anti-Pattern #2 Lost Collection Proxy on Owning SideTuesday, November 22, 2011
  43. 43. Lost Collection Proxy • Description –On the owning side of an association, we assign a new collection object to a persistent field/property overriding a collection proxy returned by hibernate • Consequences –The entire collection is re-created: one delete to remove all elements and then many element inserts 29Tuesday, November 22, 2011
  44. 44. Lost Collection Proxy - Example @Entity public class Hydra { @Id @GeneratedValue private Long id; @OneToMany(cascade=CascadeType.ALL) private List<Head> heads = new ArrayList<Head>(); public Long getId() {...} protected void setId() {...} public List<Head> getHeads() { return heads; } public void setHeads(List<Head> heads) { this.heads = heads; } } 30Tuesday, November 22, 2011
  45. 45. Lost Collection Proxy - Solution • Operate on collection objects returned by hibernate –In most cases it’s a much more efficient solution • Unless you know what you’re doing –It might be performance-wise in some cases to re- create the entire collection (bulk delete) –However, it’s the place when hibernate could do better, having all required data available: • Original size, added and removed elements • Min(#added + #removed, 1 + #size - #removed + #added) 31Tuesday, November 22, 2011
  46. 46. Puzzle #3 Fashionable DeveloperTuesday, November 22, 2011
  47. 47. Fashionable Developer @Entity public class Developer { @Id @GeneratedValue private Long id; private String mainTechnology; public boolean likesMainTechnology() { return "hibernate".equalsIgnoreCase(mainTechnology); } } // creates and persists a developer that uses hibernate as mainTechnology // new EntityManager and new transaction Developer dev = em.find(Developer.class, id); boolean foundCoolStuff = false; for (String tech : new String[]{"HTML5", "Android", "Scala"}) { dev.setMainTechnology(tech); // othersAreUsingIt: // select count(*) from Developer where mainTechnology = ? and id != ? if (othersAreUsingIt(tech, dev) && dev.likesMainTechnology()) { foundCoolStuff = true; break; } } if (!foundCoolStuff) { // still use hibernate dev.setMainTechnology("hibernate"); 33 }Tuesday, November 22, 2011
  48. 48. How Many Queries in 2nd Tx? @Entity public class Developer { (a) 2 select @Id @GeneratedValue (b) 4 selects private Long id; private String mainTechnology; (c) 4 selects, 1 update (d) 4 selects, 4 updates public boolean likesMainTechnology() { (e) None of the above return "hibernate".equalsIgnoreCase(mainTechnology); } } // creates and persists a developer that uses hibernate as mainTechnology // new EntityManager and new transaction Developer dev = em.find(Developer.class, id); boolean foundCoolStuff = false; for (String tech : new String[]{"HTML5", "Android", "Scala"}) { dev.setMainTechnology(tech); // othersAreUsingIt: // select count(*) from Developer where mainTechnology = ? and id != ? if (othersAreUsingIt(tech, dev) && dev.likesMainTechnology()) { foundCoolStuff = true; break; } } if (!foundCoolStuff) { // still use hibernate dev.setMainTechnology("hibernate"); 34 }Tuesday, November 22, 2011
  49. 49. How Many Queries in 2nd Tx? (a) 2 selects (b) 4 selects (c) 4 selects, 1 update (d) 4 selects, 4 inserts (e) None of the above Hibernate must guarantee correctness of executed queries, therefore in certain situations it must perform flushes during a transaction. 35Tuesday, November 22, 2011
  50. 50. Fashionable Developer @Entity public class Developer { @Id @GeneratedValue private Long id; private String mainTechnology; NO UPDATES public boolean likesMainTechnology() { return "hibernate".equalsIgnoreCase(mainTechnology); } } // creates and persists a developer that uses hibernate as mainTechnology // new EntityManager and new transaction Developer dev = em.find(Developer.class, id); boolean foundCoolStuff = false; for (String tech : new String[]{"HTML5", "Android", "Scala"}) { dev.setMainTechnology(tech); // othersAreUsingIt: // select count(*) from Developer where mainTechnology = ? and id != ? if (/*othersAreUsingIt(tech, dev) &&*/ dev.likesMainTechnology()) { foundCoolStuff = true; break; } } if (!foundCoolStuff) { // still use hibernate dev.setMainTechnology("hibernate"); 36 }Tuesday, November 22, 2011
  51. 51. Anti-Pattern #3 Temporary ChangesTuesday, November 22, 2011
  52. 52. Temporary Changes • Description –We change the persistent data of an object temporarily to test some features –In the meantime a database flush occurs triggered, for example, by a HQL touching the table • Consequences –Flushes can be performed during the transaction, not only at the commit time –Temporary changes persisted into the database unnecessarily • Solution –Plan your business model and processing to avoid temporary changes to your persistent data 38Tuesday, November 22, 2011
  53. 53. Puzzle #4 Plant a TreeTuesday, November 22, 2011
  54. 54. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany Collection<Tree> trees = new HashSet<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction Tree tree = new Tree(“oak”); em.persist(tree); Forest forest = em.find(Forest.class, id); forest.plantTree(tree); 40Tuesday, November 22, 2011
  55. 55. How Many Queries in 2nd Tx? @Entity (a) 1 select, 2 inserts public class Forest { (b) 2 selects, 2 inserts @Id @GeneratedValue (c) 2 selects, 1 delete, private Long id; @OneToMany 10.000+2 inserts Collection<Tree> trees = new HashSet<Tree>(); (d) Even more ;-) public void plantTree(Tree tree) { trees.add(tree); } } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction Tree tree = new Tree(“oak”); em.persist(tree); Forest forest = em.find(Forest.class, id); forest.plantTree(tree); 41Tuesday, November 22, 2011
  56. 56. How Many Queries in 2nd Tx? (a) 1 select, 2 inserts (b) 2 selects, 2 inserts (c) 2 selects, 1 delete, 10.000+2 inserts (d) Even more ;-) The combination of OneToMany and Collection enables a bag semantic. That’s why the collection is re-created. 42Tuesday, November 22, 2011
  57. 57. Plant a Tree - Revisited @Entity public class Orchard { @Id @GeneratedValue private Long id; @OneToMany List<Tree> trees = new ArrayList<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction Tree tree = new Tree(“apple tree”); em.persist(tree); Orchard orchard = em.find(Orchard.class, id); orchard.plantTree(tree); 43Tuesday, November 22, 2011
  58. 58. Plant a Tree - Revisited @Entity public class Orchard { STILL BAG SEMANTIC! @Id @GeneratedValue private Long id; @OneToMany List<Tree> trees = new ArrayList<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction Tree tree = new Tree(“apple tree”); em.persist(tree); Orchard orchard = em.find(Orchard.class, id); orchard.plantTree(tree); 43Tuesday, November 22, 2011
  59. 59. Plant a Tree - Revisited @Entity public class Orchard { STILL BAG SEMANTIC! @Id @GeneratedValue private Long id; Use OrderColumn or @OneToMany List<Tree> trees = new ArrayList<Tree>(); IndexColumn for list semantic. public void plantTree(Tree tree) { trees.add(tree); } } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction Tree tree = new Tree(“apple tree”); em.persist(tree); Orchard orchard = em.find(Orchard.class, id); orchard.plantTree(tree); 43Tuesday, November 22, 2011
  60. 60. OneToMany Mapping Seman&c Java  Type Annota&on java.u3l.Collec3on bag  seman3c java.u3l.List @ElementCollec3on  || @OneToMany  ||  @ManyToMany set  seman3c java.u3l.Set @ElementCollec3on  || @OneToMany  ||  @ManyToMany (@ElementCollec3on  || @OneToMany  ||  @ManyToMany)   list  seman3c java.u3l.List && (@OrderColumn  ||   @IndexColumn) @OneToMany  (no  cascade  op3on) 44Tuesday, November 22, 2011
  61. 61. OneToMany Mapping add   remove   update   element element element bag   re-­‐create: re-­‐create: 1  update seman3c 1  delete  +  N  inserts 1  delete  +  N  inserts set   1  insert 1  delete 1  update seman3c list   1  insert  +  M   1  delete  +  M   1  update seman3c updates updates* @OneToMany  (no  cascade  op3on) 45Tuesday, November 22, 2011
  62. 62. OneToMany Mapping add   remove   update   element element element bag   re-­‐create: re-­‐create: 1  update seman3c 1  delete  +  N  inserts 1  delete  +  N  inserts set   1  insert 1  delete 1  update seman3c list   1  insert  +  M   1  delete  +  M   1  update seman3c updates updates* @OneToMany  (no  cascade  op3on) 46Tuesday, November 22, 2011
  63. 63. OneToMany Mapping add   remove   update   element element element Oops, we have a problem. bag   (list: removal of nth element, n < size-2) re-­‐create: re-­‐create: seman3c 1  delete  +  N  inserts 1  delete  +  N  inserts 1  update set   1  insert 1  delete 1  update seman3c list   1  insert  +  M   1  delete  +  M   1  update seman3c updates updates* @OneToMany  (no  cascade  op3on) 47Tuesday, November 22, 2011
  64. 64. Anti-Pattern #4 Inadequate Collection Type (Owning Side)Tuesday, November 22, 2011
  65. 65. Inadequate Collection Mapping (Owning Side) • Description –Chosen an inadequate collection mapping on the owning side • Consequences –Additional queries executed • Solution –Consider your use cases and usage patterns and choose a mapping with the least performance overhead 49Tuesday, November 22, 2011
  66. 66. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany Set<Tree> trees = new HashSet<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction Tree oak = new Tree(“oak”); em.persist(oak); Forest forest = em.find(Forest.class, id); forest.plantTree(oak); 50Tuesday, November 22, 2011
  67. 67. Anti-Pattern #5 OneToMany as Owning SideTuesday, November 22, 2011
  68. 68. OneToMany as Owning Side • Description –OneToMany used as the owning side of a relationship • Consequences –Collection elements loaded into memory –Possibly unnecessary queries –Transaction and locking schema problems: version, optimistic locking • Solution –Use ManyToOne as the owning side and OneToMany as the inverse side –Or at least exclude the collection from locking • @OptimisticLock(excluded=true) . 52Tuesday, November 22, 2011
  69. 69. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany (mappedBy = “forest”) Set<Tree> trees = new HashSet<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } @Entity public class Tree { @Id @GeneratedValue private Long id; private String name; @ManyToOne Forest forest; public void setForest(Forest forest) { this.forest = forest; this.forest.plantTree(this); } } 53Tuesday, November 22, 2011
  70. 70. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany (mappedBy = “forest”) Set<Tree> trees = new HashSet<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } @Entity public class Tree { @Id @GeneratedValue private Long id; private String name; @ManyToOne Forest forest; public void setForest(Forest forest) { this.forest = forest; this.forest.plantTree(this); } } 54Tuesday, November 22, 2011
  71. 71. Anti-Pattern #6 Inadequate Collection Type (Inverse Side)Tuesday, November 22, 2011
  72. 72. Inadequate Collection Type (Inverse Side) • Description –Set used as a collection type on the inverse side of a relationship and, to keep the model consistent, the owning side updates the inverse side • Consequences –Due to a set semantic, all elements must be loaded when we add a new element • Solution –Use Collection or List instead 56Tuesday, November 22, 2011
  73. 73. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany (mappedBy = “forest”) Collection<Tree> trees = new HashSet<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } @Entity public class Tree { @Id @GeneratedValue private Long id; private String name; @ManyToOne Forest forest; public void setForest(Forest forest) { this.forest = forest; this.forest.plantTree(this); } } 57Tuesday, November 22, 2011
  74. 74. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany (mappedBy = “forest”) Collection<Tree> trees = new HashSet<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } @Entity public class Tree { @Id @GeneratedValue private Long id; private String name; @ManyToOne Forest forest; // ... } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction em.remove(forest); 58Tuesday, November 22, 2011
  75. 75. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany (mappedBy = “forest”) Collection<Tree> trees = new HashSet<Tree>(); public void plantTree(Tree tree) { trees.add(tree); } } @Entity public class Tree { @Id @GeneratedValue private Long id; private String name; @ManyToOne Forest forest; // ... } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction em.remove(forest); 58Tuesday, November 22, 2011
  76. 76. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany (mappedBy = “forest”) Collection<Tree> trees = new HashSet<Tree>(); // ... } @Entity public class Tree { @Id @GeneratedValue private Long id; private String name; @ManyToOne Forest forest; // ... } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction for (Tree tree : forest.getTrees()) { tree.setForest(null); } 59 em.remove(forest);Tuesday, November 22, 2011
  77. 77. Plant a Tree @Entity public class Forest { @Id @GeneratedValue private Long id; @OneToMany (mappedBy = “forest”) Collection<Tree> trees = new HashSet<Tree>(); // ... } @Entity public class Tree { @Id @GeneratedValue private Long id; 10.000 UPDATES private String name; @ManyToOne 1 DELETE Forest forest; // ... } // creates and persists a forest with 10.000 trees // new EntityManager and new transaction for (Tree tree : forest.getTrees()) { tree.setForest(null); } 59 em.remove(forest);Tuesday, November 22, 2011
  78. 78. Anti-Pattern #7 One by One ProcessingTuesday, November 22, 2011
  79. 79. Inadequate Collection Type (Inverse Side) • Description –Sequential processing of a persistent collection/objects • Consequences –Each database operation performed separately for each element • Solution –Bulk queries –That’s why CaveatEmptor was implemented like this (aggregate function on a database level) 61Tuesday, November 22, 2011
  80. 80. Conclusions • Big data cause big problems –Standard mappings don’t handle large datasets well –Smart model, bulk processing, projections • RTFM –Most of information can be found in the hibernate docs –Understand what you read –Think about consequences –And hopefully you’ll be fine :) • Hibernate –Smarter policies and data structures 62Tuesday, November 22, 2011
  81. 81. Contact • email: patrycja@yonita.com • twitter: @yonlabs • www: http://www.yonita.com 63Tuesday, November 22, 2011
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