Reactive Transactions Masterclass

Joined talk with Mark Paluch (http://twitter.com/mp911de, https://speakerdeck.com/mp911de) at Devoxx 2019.

How are reactive transactions supposed to work in a non-blocking, reactive application? Spring draws with its reactive transaction manager a new, strong primitive in the picture of reactive systems.

We will deeply dive into Reactive Relational Database Connectivity, the reactive specification for SQL database access and into Neo4j 4 that comes with a reactive database client. We will walk through the access of strictly transactional data sources while embracing reactive and non-blocking properties.

This highly technical Deep Dive session will visit reactive patterns for potentially highly concurrent applications that are no longer opinionated about threading.

Come to this session and learn how to set up and use transactions in a reactive application. We will present R2DBC and Neo4j examples and are open for questions, comments, and discussion.

Transcript

1. @mp911de and @rotnroll666 #Devoxx #ReactiveProgramming Reactive transaction masterclass Mark Paluch, Pivotal. Michael Simons, Neo4j, Inc.
2. #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
3. #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
4. #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
5. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative Transactions
6. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Regular transaction
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13. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Phantom read
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28. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 No rollback / Duplication
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34. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Broken transaction
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44. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction • Atomically apply changes • Isolation • Consistency • Durable • Require a transactional resource
45. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Resource-local Transaction • Allocate transactional resource • Apply work • Cleanup transaction
46. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Database Example • Open connection • Begin transaction • Apply work • Reuse same connection across operations • Commit/rollback transaction
47. Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666
48. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Attributes • Isolation Level • Explicit Commit Mode • Read-Only Optimizations
49. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Management • Ensures transactional behaviour • Apply transaction definition (propagation, attributes) • Implementations • JTA • Spring • Driver-specific
50. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Managers •DataSourceTransactionManager •MongoTransactionManager •Neo4jTransactionManager
51. #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
52. Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Transactional
53. #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
54. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative Transactions • Stay on a single thread* • ThreadLocal storage • Using another thread breaks transactions * ManagedExecutorService, @Async
55. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative transactions are fully synchronous
56. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time-dependency in transactions
57. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time dependency • Begin Tx before work • Work after begin Tx • Work before cleanup Tx • Cleanup Tx after work
58. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Distributed Transactions
59. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666
60. #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
61. #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
62. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive Transactions
63. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Database • Open connection • Begin transaction • Apply work • Reuse same connection across operations • Commit/rollback transaction
64. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Transaction Managers •R2dbcTransactionManager •Neo4jTransactionManager •MongoTransactionManager
65. #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
66. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive transactions are fully synchronous
67. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive transactions are non-blocking
68. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time-dependency in transactions
69. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Time dependency • Begin before work • Work after begin • Work before cleanup • Cleanup after work
70. #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
71. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Cancelation (Connection Terminated while Processing)
72. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666
73. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) (Server)
74. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)
75. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)
76. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)
77. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)
78. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server) ✂
79. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server) ✂
80. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server) ✂
81. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)
82. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)
83. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 (Client) POST /some/data (Server)
84. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 More on cancelation
85. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Cancellation • .first(), .take(n) • Send cancellation signal upstream • „Thank you I don’t need additional data“ • „Connection dead. Cancelling“
86. #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
87. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 // Define a flow that creates 1000 nodes in a database Flux<Integer> 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?
88. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 // Just take some of those createNodes.take(5); „Cancelled subscription does not await completion“ What does that even mean?
89. #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?
90. #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?
91. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Depends
92. #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)
93. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 R2DBC
94. #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
95. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Dependencies • Reactive Streams • Java 8
96. #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
97. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 SPI • ConnectionFactory • Connection • Statement • Result • Row
98. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Drivers • H2 • Google Cloud Spanner • MySQL • Postgres • SQL Server • SAP Hana
99. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ConnectionFactory Transactions • Publisher<Void> beginTransaction(); • Publisher<Void> commitTransaction(); • Publisher<Void> rollbackTransaction();
100. Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666
101. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Data R2DBC •R2dbcTransactionManager
102. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Framework 5.2 • Reactive Transaction Manager SPI • Support for @Transactional • TransactionalOperator
103. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Transactional • Method signature declares known reactive type • Requires ReactiveTransactionManager • Code path for reactive transaction management • Otherwise • Uses PlatformTransactionManager
104. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Data R2DBC • Demo @Transactional • Demo TransactionalOperator
105. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Data escape • Transactional data escapes before transaction completion • Demo
106. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Neo4j
107. #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
108. #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
109. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 The whiteboard model IS the physical model • Just fill the abstract nodes with content
110. Demo #Devoxx #ReactiveProgramming @mp911de and @rotnroll666
111. #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
112. #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
113. #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
114. #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
115. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Challenges • Driver shall provide a similar surface for various languages • Java • JavaScript • Python • .NET
116. #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
117. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Imperative Transactions
118. #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
119. #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
120. #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
121. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Reactive Transactions
122. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 RxSession session = driver.rxSession(); Publisher<RxTransaction> txPublisher = session.beginTransaction(); RxTransaction tx; RxStatementResult result = tx.run(); Publisher<Record> recordPublisher = result.records() Publisher<Void> commit = tx.commit(); Publisher<Void> rollback = tx.rollback(); Reactive surface
123. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void implicit() { Flux<Long> 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
124. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void txFunctions() { RxTransactionWork<Publisher<Long>> 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<Long> personCreation = Flux.using(driver::rxSession, session -> session.writeTransaction(txFunction), RxSession::close); StepVerifier.create(personCreation) .expectNextCount(1) .verifyComplete(); } Transactional functions
125. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Test void explicit() { Function<RxSession, Flux<Long>> 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<Long> personCreation = Flux.using(driver::rxSession, actualWork, RxSession::close); } Explicit
126. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Spring Data Neo4j⚡RX (SDN/RX)
127. #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
128. #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
129. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jClient reactiveClient; Flux<Map<String, Object>> 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?
130. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTemplate reactiveTemplate; Flux<MovieEntity> movies = reactiveTemplate .findAll(MovieEntity.class); SDN/RX how does it look?
131. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 public interface MovieRepository extends ReactiveNeo4jRepository<MovieEntity, String> { Mono<MovieEntity> findOneByTitle(String title); } SDN/RX how does it look?
132. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 @Service public class MovieService { @Transactional public Flux<MovieEntity> doSomething() { // Return type indicating reactive or imperative return Flux.empty(); } void doSomethingElse() { ReactiveNeo4jTemplate reactiveTemplate; TransactionalOperator transactionalOperator; Flux<MovieEntity> movies = transactionalOperator.transactional( reactiveTemplate.findAll(MovieEntity.class) ); } } And transactions?
133. #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
134. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: Function<RxSession, Flux<Long>> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux<Long> completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)
135. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition Function<RxSession, Flux<Long>> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux<Long> completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)
136. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction Function<RxSession, Flux<Long>> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux<Long> completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)
137. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction • Executing stuff Function<RxSession, Flux<Long>> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux<Long> completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)
138. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction • Executing stuff • Commit or rollback Function<RxSession, Flux<Long>> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux<Long> completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)
139. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 ReactiveNeo4jTransactionManager • Basically this, in a Spring way: • Session acquisition • Starting transaction • Executing stuff • Commit or rollback • Closing session Function<RxSession, Flux<Long>> actualWork = session -> Flux.usingWhen( session.beginTransaction(), tx -> Flux.just(1L), RxTransaction::commit, (tx, e) -> tx.rollback(), RxTransaction::commit); Flux<Long> completeUnitOfWork = Flux.using(driver::rxSession, actualWork, RxSession::close)
140. #Devoxx #ReactiveProgramming @mp911de and @rotnroll666 Neo4j resources
141. #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
142. #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/
143. #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/