Java Web Programming on Google Cloud Platform [2/3] : Datastore
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Java Web Programming on Google Cloud Platform [2/3] : Datastore

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Java Web Programming on Google App Engine, July 2012

Java Web Programming on Google App Engine, July 2012

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  • 1. Introduction to DatastoreAssoc.Prof. Dr.Thanachart Numnonda Asst.Prof. Thanisa Kruawaisayawan www.imcinstitute.com July 2012
  • 2. AgendaWhat is DataStore?Using DataStoreJPA in DataStore
  • 3. What is DataStore?
  • 4. What is Datastore?Google App Engine Datastore is a schema-less persistence system, whose fundamental persistence unit is called Entity, c omposed by an immutable Key and a collection of mutable pr operties.Entities can be created, updated, deleted, loaded by key and queried for properties values.DataStore is consistent and transactional, with support to current transaction.
  • 5. The DataStoreThe Datastore is not a relational database nor a façade.Relational database technology doesn’t scale horizontally – Connection pools, shared caching are a problemThe Datastore is one of many public APIs used for accessing Google’s
  • 6. The DataStore
  • 7. The DataStore
  • 8. The DataStore : OperationsTransactions and Index are based on MegaTable.File persistence its done with Google File System (GFS).Its distributed by Chubby, a lock service for loosely- coupled distributed systems.
  • 9. BigTableBigTable is a compressed, high performance, and proprietary database system built on Google File System (GFS), Chubby Lock Service, and a few other Google programsCurrently not distributed or used outside of Google.BigTable development began in 2004. and is now used by a number of Google application Google Earth, Google Map, Gmail, Youtube, etc..
  • 10. BigTable : DesignBigTable is a fast and extremely large-scale DBMS.It is a sparse, distributed multi-dimensional sorted map, sharing characteristics of both row-oriented and column- oriented databases. sparse because only "not null" values are persisted distributed in Google cloud persistent on Google File System multidimensional in columns values ordered lexicographically by key
  • 11. BigTable : DesignTables are optimized for GFS by being split into multiple tablets - segments of the table.BigTable is designed to scale into the petabyte.Each table has multiple dimensions (one of which is a feld for time, allowing for versioning and garbage collection).It allows an infnite number of rows and columns.
  • 12. Google File SystemGFS is a proprietary distributed fle system developed by Google.It is designed to provide effcient, reliable access to data using large clusters of commodity hardware.GFS grew out of an earlier Google effort, BigFiles, developed by Larry Page and Sergey Brin in the early days of Google, while it was still located in Stanford.
  • 13. Using DataStore
  • 14. DataStore OperationsDatastore operations are defned around entities (data models) which are objects with one or more properties Types: string, user, Boolean, and so on Entities may be recursive or self-referentialEntity relationships are one-to-many or many-to-many.Entities may be fxed or grow as needed.
  • 15. DataStore Storage ModelEvery entity is of a particular kindEntities in a kind need not have the same properties One entity may have different “columns” from another in the same kind!Unique IDs are automatically assigned unless the user defnes a key_name
  • 16. Compare DataStore with Others
  • 17. DataStore Storage ModelBasic unit of storage is an Entity consisting of Kind (table) Key (primary key) Entity Group (partition) 0..N typed Properties (columns)
  • 18. Datastore QuotasEach call to Datastore counts towards the quotaThe amount of data cannot exceed the billable  Includes properties and keys but not the indicesCPU and Datastore CPU time quotas apply
  • 19. Using the DatastoreApplications may access the Datastore using the JDO or the JPA classes.The JDO and JPA classes are abstracted using the DataNucleus API Open source  Not very popular  Support for Java standards  Poor documentation
  • 20. JPA in DataStore
  • 21. Setting Up JPAThe JPA and datastore JARs must be in the apps war/WEB-INF/lib/ directory.A confguration fle named persistence.xml must be in the apps war/WEB-INF/classes/META-INF/ directory,A confguration fle tells JPA to use the App Engine datastore.The appengine-api.jar must also be in the war/WEB- INF/lib/ directory.
  • 22. persistence.xml: Example<?xml version="1.0" encoding="UTF-8"?> <?xml version="1.0" encoding="UTF-8"?><persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" <persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"> http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"> <persistence-unit name="thaijavaappPU" transaction-type="RESOURCE_LOCAL"> <persistence-unit name="thaijavaappPU" transaction-type="RESOURCE_LOCAL"> <provider>org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider <provider>org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider </provider> </provider> <non-jta-data-source/> <non-jta-data-source/> <properties> <properties> <property name="datanucleus.ConnectionURL" value="appengine"/> <property name="datanucleus.ConnectionURL" value="appengine"/> <property name="datanucleus.NontransactionalRead" value="true"/> <property name="datanucleus.NontransactionalRead" value="true"/> <property name="datanucleus.NontransactionalWrite" value="true"/> <property name="datanucleus.NontransactionalWrite" value="true"/> </properties> </properties> </persistence-unit> </persistence-unit></persistence> </persistence>
  • 23. Getting an EntityManager InstanceAn app interacts with JPA using an instance of the EntityManager.import javax.persistence.EntityManagerFactory; import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence; import javax.persistence.Persistence;public class EMF {{ public class EMF private static final EntityManagerFactory emfInstance == private static final EntityManagerFactory emfInstance Persistence.createEntityManagerFactory("transactions-optional"); Persistence.createEntityManagerFactory("transactions-optional"); public static EntityManagerFactory get() {{ public static EntityManagerFactory get() return emfInstance; return emfInstance; }}}}
  • 24. Entity Class : Example@Entity @Entitypublic class GuestList implements Serializable {{ public class GuestList implements Serializable …… @Id @Id private String id; private String id; @Basic @Basic private User author; private User author; private String content; private String content; @Temporal(javax.persistence.TemporalType.DATE) @Temporal(javax.persistence.TemporalType.DATE) private Date visitDate; private Date visitDate; …… // Getter and Setter methods // Getter and Setter methods}}
  • 25. Queries and IndicesA query operates on every entity of a given kind. Specify zero or more sort orders Specify zero or more flters on property valuesIndices are defned in the App Engine confguration fles Results are fetched directly from these indices; no indices are created on the fly WEB-INF/datastore-indexes.xml - non-standard flesNormalization is not recommended Optimization techniques for RDBMSs may result in poor Datastore performance!
  • 26. Query : ExampleEntityManager em == EMF.get().createEntityManager(); EntityManager em EMF.get().createEntityManager();try {{ try Query query == em.createQuery("SELECT oo FROM GuestList AS o"); Query query em.createQuery("SELECT FROM GuestList AS o"); @SuppressWarnings("unchecked") @SuppressWarnings("unchecked") List<GuestList> results == (List<GuestList>) query.getResultList(); List<GuestList> results (List<GuestList>) query.getResultList(); for (Object obj :: results) {{ for (Object obj results) GuestList guest == (GuestList) obj; GuestList guest (GuestList) obj; String nickname == guest.getAuthor().getNickname(); String nickname guest.getAuthor().getNickname(); out.println(nickname ++ "" "" ++ guest.getId()); out.println(nickname guest.getId()); }}}} catch(Exception ex) {{ catch(Exception ex) out.println(ex); out.println(ex);}}
  • 27. Entity RelationshipsModels association between entities.There are four types of relationship multiplicities: @OneToOne @OneToMany @ManyToOneSupports unidirectional as well as bidirectional relationships Unidirectional relationship: Entity A references B, but B doesnt reference A.
  • 28. Example : ManyToOne Mapping
  • 29. Example : OneToMany Mapping
  • 30. Transactions and Entity GroupsTransaction = Group of Datastore operations that either succeed or failEntity groups are required because all grouped entities are stored in the same Datastore nodeAn entity may be either created or modifed once per transactionTransactions may fail if a different user or process tries an update in the same group at the same timeUsers decide whether to retry or roll the transaction back
  • 31. Transaction in JPA : ExampleBook book == em.find(Book.class, "9780596156732"); Book book em.find(Book.class, "9780596156732");BookReview bookReview == new BookReview(); BookReview bookReview new BookReview();bookReview.rating == 5; bookReview.rating 5;book.getBookReviews().add(bookReview); book.getBookReviews().add(bookReview);Transaction txn == em.getTransaction(); Transaction txn em.getTransaction();txn.begin(); txn.begin();try {{ try book == em.merge(book); book em.merge(book); txn.commit(); txn.commit();}} finally {{ finally if (txn.isActive()) {{ if (txn.isActive()) txn.rollback(); txn.rollback(); }}}}
  • 32. Unsupported Features of JPAOwned many-to-many relationships, and unowned relationships."Join" queries.Aggregation queries (group by, having, sum, avg, max, min)Polymorphic queries.
  • 33. ResourcesGoogle App Engine for Java HOWTO, Andrew Lombardi, Mar 2010The Softer Side Of Schemas, Max Ross, May 2009Official Google App Engine Tutorial, http://code.google.com/appengine/docs/java/gettingstarted/Programming Google App Engine, Don Sanderson, OReilly, 2010
  • 34. Thank you thananum@gmail.comwww.facebook.com/imcinstitute www.imcinstitute.com