Reactive Transactions Masterclass

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@mp911de and @rotnroll666 #Devoxx #ReactiveProgramming Reactive transaction masterclass Mark Paluch, Pivotal. Michael Simons, Neo4j, Inc.

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Mark Paluch • Spring Data Project Lead • Lettuce Redis Driver Project Lead • R2DBC Contributor • All things Reactive Data & Open Source github.com/mp911de • @mp911de • paluch.biz

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Michael Simons • Neo4j since July 2018 • Java Champion and Oracle Groundbreaker • Co-Founder and current lead of Java User Group EuregJUG • Author

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 More books: Life behind bars • I run… • I bike… • …and take pictures Revenue will go to Médecins Sans Frontières msf.org this year https://leanpub.com/lifebehindbars

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative Transactions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Regular transaction

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 [ ]

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Phantom read

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 No rollback / Duplication

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Broken transaction

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction • Atomically apply changes • Isolation • Consistency • Durable • Require a transactional resource

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Resource-local Transaction • Allocate transactional resource • Apply work • Cleanup transaction

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Database Example • Open connection • Begin transaction • Apply work • Reuse same connection across operations • Commit/rollback transaction

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Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Attributes • Isolation Level • Explicit Commit Mode • Read-Only Optimizations

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Management • Ensures transactional behaviour • Apply transaction deﬁnition (propagation, attributes) • Implementations • JTA • Spring • Driver-speciﬁc

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Managers •DataSourceTransactionManager •MongoTransactionManager •Neo4jTransactionManager

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Walkthrough • Allocate connection • Bind connection to transaction (Thread*) • Prepare connection for transaction (isolation level, …) • Issue queries (Reuse bound connection) • Exit transactional scope • Cleanup, commit or rollback • Run synchronizations • Unbind resources

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Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Transactional

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Bound connection • Transactional state associated with transport connection • Works since the ’70s like that • Alternatively: Session • Newer implementations: Portable session • MongoDB

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative Transactions • Stay on a single thread* • ThreadLocal storage • Using another thread breaks transactions * ManagedExecutorService, @Async

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative transactions are fully synchronous

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time-dependency in transactions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time dependency • Begin Tx before work • Work after begin Tx • Work before cleanup Tx • Cleanup Tx after work

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Distributed Transactions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Distributed Transactions • XA speciﬁcation • Released in the 90’s • Transactions across distributed services • Two phase commit • Turned out that it sucks

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Still Distributed Transactions • Redis + JDBC Transaction • Kind-of works • Leading transaction manager • Additional transactional resources may join • Independent commit/rollback • Still sucks

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive Transactions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Database • Open connection • Begin transaction • Apply work • Reuse same connection across operations • Commit/rollback transaction

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Managers •R2dbcTransactionManager •Neo4jTransactionManager •MongoTransactionManager

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Walkthrough • Allocate connection • Bind connection to transaction (Subscription) • Prepare connection for transaction (isolation level, …) • Issue queries (Reuse bound connection) • Exit transactional scope • Cleanup, commit or rollback • Run synchronizations • Unbind resources

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive transactions are fully synchronous

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive transactions are non-blocking

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time-dependency in transactions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time dependency • Begin before work • Work after begin • Work before cleanup • Cleanup after work

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative vs. Reactive • Single-threaded processing required • ThreadLocal transaction status • Data stays within transactional bounds • Synchronized begin and cleanup • Multi-threaded processing possible • Subscription-bound transaction status • Data escapes transactional bounds • Synchronized begin and cleanup

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Cancelation (Connection Terminated while Processing)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server) ✂

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server) ✂

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server) ✂

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 More on cancelation

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Cancellation • .first(), .take(n) • Send cancellation signal upstream • „Thank you I don’t need additional data“ • „Connection dead. Cancelling“

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Cancellation effects • Cancellation considered success • Cancelled subscription does not await completion • Commit may be not yet visible to subsequent operations

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 // Define a flow that creates 1000 nodes in a database Flux createNodes = Flux.using( driver::rxSession, session -> session.run( "UNWIND range (1,1000) AS i CREATE (s:SomeNode {pos: i}) return s").records(), RxSession::close ).map(r -> r.get("s").get("pos").asInt()); „Cancelled subscription does not await completion“ What does that even mean?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 // Just take some of those createNodes.take(5); „Cancelled subscription does not await completion“ What does that even mean?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 // Or more explicit createNodes .as(StepVerifier::create) .expectNext(1, 2, 3, 4, 5) .thenCancel() .verify(); „Cancelled subscription does not await completion“ What does that even mean?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 // Can we verify it? Flux.using( driver::rxSession, session -> session.run("MATCH (s:SomeNode) RETURN count(s) as cnt").records(), RxSession::close ) .map(r -> r.get("cnt").asLong()) .single().as(StepVerifier::create).expectNext(1000L).verifyComplete(); „Cancelled subscription does not await completion“ What does that even mean?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Depends

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Cancellation • Happens when the browser goes away • Probably not a good idea to return transactional ﬂows from web endpoints (The same has been said for @Transactional on web methods for a long time!) • Again: .first(), .take(n) • Also limitRequest(n)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 R2DBC

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive Relational Database Connectivity • A speciﬁcation designed from the ground up for reactive programming • End to end reactive and non-blocking

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Dependencies • Reactive Streams • Java 8

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Design Principles • Embrace Reactive Types and Patterns • Non-blocking, all the way to the database • Documented speciﬁcation • Shrink the driver SPI • Enable multiple "humane" APIs

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 SPI • ConnectionFactory • Connection • Statement • Result • Row

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Drivers • H2 • Google Cloud Spanner • MySQL • Postgres • SQL Server • SAP Hana

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ConnectionFactory Transactions • Publisher beginTransaction(); • Publisher commitTransaction(); • Publisher rollbackTransaction();

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Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Data R2DBC •R2dbcTransactionManager

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Framework 5.2 • Reactive Transaction Manager SPI • Support for @Transactional • TransactionalOperator

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Transactional • Method signature declares known reactive type • Requires ReactiveTransactionManager • Code path for reactive transaction management • Otherwise • Uses PlatformTransactionManager

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Data R2DBC • Demo @Transactional • Demo TransactionalOperator

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Data escape • Transactional data escapes before transaction completion • Demo

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Neo4j

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 What is Neo4j? • A (property) graph database • An ecosystem • I work on Spring and Spring Data integration as part of the drivers team

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 A Property Graph :Movie :Person :Person Nodes represents objects (Nouns) :DIRECTED :ACTED_IN role: someRole name: someName Relationships connect nodes and represent actions (verbs) Both nodes and relationships can have properties

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 The whiteboard model IS the physical model • Just ﬁll the abstract nodes with content

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Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Neo4j 4.0 • Reactive Cypher engine • Reactive Driver available (Beta) • Spring Data Neo4j RX (Public preview) • Imperative and reactive transaction managers

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Building blocks of Neo4j driver Driver Top level object for all Neo4j interaction Session Logical context for sequence of transactions Transaction Unit of work Statement result Stream of records plus metadata

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Building blocks of Neo4j driver Driver Session Connection pool Connection Connection Server A Server B spawns borrows owns owns to

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Building blocks of Neo4j driver • Session is a logical concept over the connection • One ongoing transaction per session • Thus, the connection is bound to the transaction

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Challenges • Driver shall provide a similar surface for various languages • Java • JavaScript • Python • .NET

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 More challenges • Already two different programming models • Imperative / Blocking • Asynchronous (Pretty much the default in .NET, feels like Co- Routines in Kotlin / Lightweight Threads in Loom) • Supported for all languages • Reactive coming up • Java • JavaScript • .NET

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative Transactions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void implicit() { // Aka "Auto-Commit" try (Session session = driver.session()) { long personId = session .run( "CREATE (a:Person {name: $name}) RETURN id(a) as id“, parameters("name", NAME)) .single().get("id").asLong(); } } Implicit

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void txFunctions() { try (Session session = driver.session()) { long personId = session.writeTransaction( tx -> tx.run( "CREATE (a:Person {name: $name}) RETURN id(a) as id“, parameters("name", NAME)) .single().get("id").asLong()); } } Transactional functions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void explicit() { try (Session session = driver.session()) { Transaction tx = session.beginTransaction(TransactionConfig.builder().build()); long personId = tx.run( "CREATE (a:Person {name: $name}) RETURN id(a) as id“, parameters("name", NAME)) .single().get("id").asLong(); tx.commit(); } } Explicit

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive Transactions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 RxSession session = driver.rxSession(); Publisher txPublisher = session.beginTransaction(); RxTransaction tx; RxStatementResult result = tx.run(); Publisher recordPublisher = result.records() Publisher commit = tx.commit(); Publisher rollback = tx.rollback(); Reactive surface

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void implicit() { Flux personCreation = Flux.using( driver::rxSession, session -> session.run( "CREATE (a:Person {name: $name}) RETURN id(a) as id“, parameters("name", NAME) ).records(), RxSession::close ).map(r -> r.get("id").asLong()); StepVerifier.create(personCreation) .expectNextCount(1) .verifyComplete(); } Implicit

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void txFunctions() { RxTransactionWork> txFunction = tx -> Flux.from(tx.run( "CREATE (a:Person {name: $name}) RETURN id(a) as id", parameters("name", NAME)).records() ) .map(r -> r.get("id").asLong()); Flux personCreation = Flux.using(driver::rxSession, session -> session.writeTransaction(txFunction), RxSession::close); StepVerifier.create(personCreation) .expectNextCount(1) .verifyComplete(); } Transactional functions

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void explicit() { Function> actualWork = session -> Flux.usingWhen(session.beginTransaction(), // Yes, this looks pretty much like the `txFunction` in the example before tx -> tx.run( "CREATE (a:Person {name: $name}) RETURN id(a) as id", parameters("name", NAME) ).records(), RxTransaction::commit, // Success case (tx, e) -> tx.rollback(), // Error / exceptional case RxTransaction::commit // Cancelation ).map(r -> r.get("id").asLong()); Flux personCreation = Flux.using(driver::rxSession, actualWork, RxSession::close); } Explicit

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Data Neo4j⚡RX (SDN/RX)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 How does SDN/RX differ from previous SDN? • Modular design • Fundamental design differences (e.g. mutability, incremental mapping) • SDN/OGM layers are now combined • Transport functionality moved entirely to Java driver • Supports all "ﬁndBy*" methods • Query by Example • Integration with Spring 5.2’s Reactive Transaction Manager

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 SDN/RX Spring Data Repositories Neo4j Template Neo4j Client Driver Neo4j „uses“ sdn-rx-spring-boot-starter neo4j-java-driver-spring-boot-starter provides provides Integration with Spring Transactions from here on SDN/RX components

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jClient reactiveClient; Flux> directorAndMovies = reactiveClient .query( "MATCH (p:Person) - [:DIRECTED] -> (m:Movie {title: $title})," + " (p) - [:WROTE] -> (om:Movie) " + "WHERE p.name =~ $name " + " AND p.born < $someDate.year " + "RETURN p, om" ) .bind(LocalDate.of(1979, 9, 21)).to("someDate") .bindAll(Map.of("title", "The Matrix", "name", "Li.*")) .fetch() .all(); SDN/RX how does it look?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTemplate reactiveTemplate; Flux movies = reactiveTemplate .findAll(MovieEntity.class); SDN/RX how does it look?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 public interface MovieRepository extends ReactiveNeo4jRepository { Mono findOneByTitle(String title); } SDN/RX how does it look?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Service public class MovieService { @Transactional public Flux doSomething() { // Return type indicating reactive or imperative return Flux.empty(); } void doSomethingElse() { ReactiveNeo4jTemplate reactiveTemplate; TransactionalOperator transactionalOperator; Flux movies = transactionalOperator.transactional( reactiveTemplate.findAll(MovieEntity.class) ); } } And transactions?

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Uses explicit reactive transactions • Uses the driver instance as lookup for the transactional resource • Stores both the session and transaction belonging to that session into resource holder

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: Function> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition Function> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction Function> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction • Executing stuff Function> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction • Executing stuff • Commit or rollback Function> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction • Executing stuff • Commit or rollback • Closing session Function> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Neo4j resources

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Neo4j • https://neo4j.com/download/ • Neo4j Desktop (Analyst centric) • Neo4j Server (Community and Enterprise Edition) Community Edition: GPLv3 Enterprise Edition: Proprietary

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Neo4j Datasets • Preconfigured instance with several different datasets https://neo4j.com/sandbox-v2/ • Neo4j Graph Gists, Example Models and Cypher Queries https://neo4j.com/graphgists/ • Panama papers and other offshore leaks https://offshoreleaks.icij.org/

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#Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring related • Neo4j Driver Spring Boot Starter https://github.com/neo4j/neo4j-java-driver-spring-boot-starter • Spring Data Neo4j⚡RX https://github.com/neo4j/sdn-rx/