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Mark Paluch
@mp911de
UNDER THE HOOD OF
REACTIVE DATA ACCESS
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Spring Data Modules
JPA
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Reactive Spring Data Modules
JPA
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What about…
JDBC?
JPA?
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Relational Databases
•Not a good fit for reactive access
•Limited scalability
•Resource synchronization
•ACID Transactions
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JDBC
•Fully blocking API
•Non-blocking API announced: ADBA
(JDK-8188051)
http://mail.openjdk.java.net/pipermail/jdbc-spec-discuss/ • JDK-8188051: http://hg.openjdk.java.net/jdk/sandbox/shortlog/JDK-8188051-branch
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Query Behavior
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Query by Time
Transport
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Synchronous Data Access
Data store
App
Data store
App
Data store
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Reactive Data Access
Data store
App
Data store Data store Data store
App
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Differences to imperative Data Access
•Drivers require threading infrastructure
•Timeout handling different
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Synchronous Timeouts
Socket.setSoTimeout(…)
⏱
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Aynchronous Timeouts
•Active timeout tracking required
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Reactive Drivers
•End-to-end nonblocking
•Asynchronous request-response processing
•Non-blocking pooling
•Non-blocking connect
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Application Driver Application
Request
Server selection
Queueing
Write Response decoding
Response buffering
Request completion Response
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Reactive NoSQL drivers
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MongoDB
•Reactive-over-async driver
•Cursor lifecycle
•Pluggable I/O
•Pooled connections
Java.NIO
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Query by Time
Request
Response
(chunk)
Response
(complete)
Prefetch
(cont.d)
Query
Emit
elements
Result
processing
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MongoDB Driver Fetching
Operator
MongoDB Subscriber
request(Long.MAX_VALUE)
request(Long.MAX_VALUE)
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MongoDB Driver Fetching
Filter
MongoDB Subscriber
request(Long.MAX_VALUE)
request(Long.MAX_VALUE)
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MongoDB Driver Fetching
Filter
MongoDB Subscriber
request(Long.MAX_VALUE)
request(1)
Dropped element
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Specific Features
•Cursor size derived from demand
•Tailable Cursors (@Tailable)
•MongoDB 3.6: Change Streams
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Redis
•Reactive driver (Lettuce 5)
•Based on Netty and Project Reactor
•Singleton connection
•Optionally: Pooled connections
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Command by Time
Request
Command
Command
(subscription)
Response
(chunk)
Response
(complete)
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Specifics
•Use ByteBuffer instead byte[]
•null handling: Emission of empty buffers
•Suspend reading if no demand
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Apache Cassandra
•Reactive bridge over async driver
•Netty-based driver (Datastax)
•Pooled connections
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Query by Time
Request
Response
(chunk)
Response
(complete)
Query
Emit
elements
Result processing
Next page
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Outlook
•Cassandra driver 4.0 in the works
•Likely support for reactive execution model
•Emit items as they are received
https://github.com/datastax/java-driver/tree/4.x • https://datastax-oss.atlassian.net/browse/JAVA-1505
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Couchbase
•Reactive driver driver
•Based on Netty and RxJava 1
•Multiple connection schemes
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Key-Value, DCP
•Request
•Response
•Emit results
Search, Query, View
•Request
•Response streaming
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Command by Time
Request
Command
Command
(subscription)
Response
(chunk)
Response
(complete)
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Outlook
•Couchbase driver likely to move to RxJava 2
•No tickets/decisions yet
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Imperative and Reactive Together
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Blocking with Imperative Programming
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Blocking with Reactive Programming
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Imperative and Reactive
@Component
public class ApplicationInitializer {
ReactiveMongoOperations ops;
@PostConstruct
public void postConstruct() {
ops.remove(Person.class).all().block();
}
}
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Imperative and Reactive
@Component
public class ApplicationInitializer {
ReactiveMongoOperations ops;
@PostConstruct
public void postConstruct() {
ops.remove(Person.class).all().block();
}
}
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Event Loop
Event Loop
(single Thread)
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Event Loop
Event Loop
(single Thread)
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Event Loop
Process next item
Callback
Register Callback
Return
Work
Database
Computation
File
I/O
Event Loop
(single Thread)
Work Queue
Work
Request Callback
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Event Loop
Process next item
Callback Work
Event Loop
(single Thread)
Work Queue
Request Callback
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Event Loop
Event Loop
(single Thread)
Work Queue Process next item
Work
Callback
Work
Wait for
Request completion
Return
Request
Request Callback
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Event Loop
Event Loop
(single Thread)
Work Queue Process next item
Work
Callback
Work
Wait for
Request completion
Return
Request
Request Callback
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Thou shalt not block
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Resources
•Slides – mp911.de/uhd-springio18
•Example Code – mp911.de/uhd-code
•Spring Data Examples – Repository @ Github
•Find us on Gitter!
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Mark Paluch
@mp911de
THANKS!