Reactive Java Programming: A new Asynchronous Database Access API by Kuassi Mensah

Copyright © 2018, Oracle and/or its affiliates. All rights reserved. |
ADBA – Asynchronous Database Access
A new asynchronous API for connecting to a database
Douglas Surber Kuassi Mensah
JDBC Architect Director, Product Management
Database Server Technologies
November, 2018

Safe Harbor Statement
The following is intended to outline our general product direction. It is intended for
information purposes only, and may not be incorporated into any contract. It is not a
commitment to deliver any material, code, or functionality, and should not be relied upon
in making purchasing decisions. The development, release, and timing of any features or
functionality described for Oracle’s products remains at the sole discretion of Oracle.
3

Program Agenda
Introduction
Code
Wrap-up
Q&A
1
2
3
4
4

ADBA – Asynchronous Database Access
• What: Java standard database access API that never blocks user threads
• Who: Developed by the JDBC Community, JDBC Expert Group and Oracle
• When: Targeted for a near future release, Java 12 perhaps
• Why: async apps have better throughput
– Fewer threads means less thread scheduling, less thread contention
– Database access is slow so blocked threads leave resources idle for a long time
5

Goals
• No user thread blocks ever
– Minimize the number of threads used for database access
• Alternate API for database access
– Not an extension to the current JDBC standard
– Not a replacement for the current JDBC standard
• Target high throughput apps
– Not a completely general purpose database access API
– At least version 1 will have a limited feature set
• Build on the Java SE class library
• Support 3rd party Reactive Stream Database Access APIs
6

Design Choices
• No reference to java.sql
• Rigorous use of types
• Builder pattern
• Fluent API
• Immutable after initialization
• One way to do something is enough
• No SQL processing by the driver
• Avoid callback hell
7

What About …?
There are already multiple async Java and JavaScript APIs
• Streams
– Java streams are inherently synchronous
• ReactiveStreams
– ADBA uses java.util.concurrent.Flow where appropriate
– R2DBC (see next slide)
• NodeJS
8

R2DBC
• Pure Reactive Streams Database Access API
– Adheres to the Reactive Manifesto
– Non-blocking Backpressure (push-pull)
– Dependency on project Reactor library
– https://github.com/r2dbc
• R2DBC over ADBA “…allows usage of ADBA drivers by using the R2DBC SPI”
– https://github.com/r2dbc/r2dbc-over-adba
– Reminder: one of the goals of ADBA is to support Reactive Streams Database Access
APIs like R2DBC
Confidential – Oracle Internal/Restricted/Highly Restricted 9
Reactive Relational Database Connectivity

Program Agenda
Introduction
Code
Wrap-up
Q&A
1
2
3
4
10

Trivial Insert
// RowCountOperation
public void insertItem(Session session, Item item) {
session.rowCountOperation("insert into tab values (:id, :name, :answer)")
.set("id", item.id(), AdbaType.NUMERIC)
.set("name", item.name(), AdbaType.VARCHAR)
.set("answer", item.answer(), AdbaType.NUMERIC)
.submit();
}

CompletionStage
java.util.concurrent.CompletionStage
• Java representation of a computational monad
• Mechanism for asynchronous programming
– Event based: push model -> higher scalability
– Allows composing asynchronous tasks
– Supports lambda expressions and fluent programming
• More @ http://bit.ly/2nnLqa0
12

Execution Model
• Everything is an Operation
• An Operation consists of
– SQL or other database operation
– Parameter assignments
– Result handling
– Submission and CompletionStage
• User thread creates and submits Operations
– Creating and submitting never blocks; user thread never blocks
• Implementation executes those Operations asynchronously
– Performs round trip(s) to the database
– Executes result handling
– Completes CompletionStage
13

getDataSource
// DataSourceFactory
public DataSource getDataSource() {
return DataSourceFactory.newFactory("oracle.database.adba")
.builder()
.url("//host.oracle.com:5521/example")
.username("scott")
.password("tiger")
.build();
}

Getting a Session
Default method in DataSource:
public default Session getSession() {
return builder().build().attach();
}
Default method in Session:
public default Session attach() {
this.submit();
this.attachOperation()
.submit();
return this;
}
15

Trivial Select
// RowOperation
public void idsForAnswer(DataSource ds, List<Integer> result, int correctAnswer) {
try (Session session = ds.getSession()) {
session.<List<Integer>>rowOperation("select id, name, answer from tab where answer = :target")
.set("target", correctAnswer, AdbaType.NUMERIC)
.collect(() -> result,
(list, row) -> list.add(row.at("id").get(Integer.class)))
.submit();
}
}

Close
@Override
public default void close() {
this.closeOperation()
.submit();
// submitting a close Operation must satisfy the requirements of
// OperationGroup.close()
}
Note: A CloseOperation is never skipped.
17

SQL Support
• All SQL is vendor specific
– No escape sequences
– No specified parameter markers
• Non vendor specific syntax requires processing by the driver
– Adds overhead
– Increases code complexity
– Minimal benefit as most apps are tied to a specific database regardless
Note: Code examples use parameter markers from a variety of databases including DB2
(:foo), MySQL (?), Oracle Database(:foo), PostgresSQL($1), SQL Server (@foo), and JDBC (?).
18

SELECT
// RowOperation
public CompletionStage<List<Item>> itemsForAnswer(DataSource ds, int answer) {
return session.<List<Item>>rowOperation("select id, name, answer from tab where answer = :target")
.set("target", 42, AdbaType.NUMERIC)
.collect(Collectors.mapping(
row -> new Item(row.at("id").get(Integer.class),
row.at("name").get(String.class),
row.at("answer").get(Integer.class)),
Collectors.toList()))
.submit()
.getCompletionStage();
}
}

Transaction
// TransactionCompletion
public void transaction(DataSource ds) {
try (Session session = ds.getSession(t -> System.out.println("ERROR: " + t.toString()))){
TransactionCompletion trans = session.transactionCompletion();
CompletionStage<Integer> idPromise = session.<Integer>rowOperation("select empno, ename from
emp where ename = :1 for update")
.set("1", "CLARK", AdbaType.VARCHAR)
.collect(Collectors.collectingAndThen(
Collectors.mapping(r -> r.at("empno").get(Integer.class),
Collectors.toList()),
l -> l.get(0)))
.onError(t -> trans.setRollbackOnly())
.submit()
continued

Transaction (continued)
session.<Long>rowCountOperation("update emp set deptno = :1 where empno = :2")
.set("1", 50, AdbaType.INTEGER)
.set("2", idPromise, AdbaType.INTEGER)
.apply(c -> {
if (c.getCount() != 1L) {
trans.setRollbackOnly();
throw new RuntimeException("updated wrong number of rows");
}
return c.getCount();
})
.onError(t -> trans.setRollbackOnly())
.submit();
// .getCompletionStage()
// .exceptionally( t -> { trans.setRollbackOnly(); return null;}) // incorrect
session.catchErrors();
session.commitMaybeRollback(trans);
}
}

OperationGroup
Operations can be grouped
• OperationGroup has its own result handling and CompletionStage
• Members submitted to group.OperationGroup submitted as a unit
• Order of execution
– Sequential in order submitted
– Parallel, any order
• Conditional or unconditional
• Error response
– Dependent: remaining group members skipped
– Independent: remaining group members unaffected
• Session is an OperationGroup
– Sequential, dependent, unconditional by default
22

Parallel UPDATE
// Parallel, Independent OperationGroup
public void updateListParallel(List<Item> list, DataSource ds) {
String query = "select id from tab where answer = :answer";
String update = "update tab set name = :name where id = :id";
try (Session session = ds.getSession();
OperationGroup<Object, Object> group = session.operationGroup()
.independent()
.parallel()) {
group.submit();
for (Item elem : list) {
CompletionStage<Integer> idPromise = group.<List<Integer>>rowOperation(query)
.set("answer", elem.answer, AdbaType.NUMERIC)
.collect(Collector.of(
() -> new ArrayList<>(),
(l, row) -> l.add(row.at("id").get(Integer.class)),
(l, r) -> l))
.submit()
.getCompletionStage()
.thenApply(l -> l.get(0));
continued

Parallel UPDATE (continued)
group.rowCountOperation(update)
.set("id", idPromise)
.set("name", "the ultimate question")
.submit()
.getCompletionStage()
.exceptionally(t -> {
System.out.println(elem.id);
return null;
});
}
}
}

Reactive Streams – Non blocking Backpressure
java.util.concurrent.Flow
ADBA User Java code

Row Publisher
// RowPublisherOperation
public CompletionStage<List<String>> rowSubscriber(DataSource ds) {
String sql = "select empno, ename from emp";
CompletableFuture<List<String>> result = new CompletableFuture<>();
Flow.Subscriber<Result.RowColumn> subscriber = new Flow.Subscriber<>() {
Flow.Subscription subscription;
List<String> names = new ArrayList<>();
int demand = 0;
@Override
public void onSubscribe(Flow.Subscription subscription) {
this.subscription = subscription;
this.subscription.request(10);
demand += 10;
}
continued

Row Publisher(continued)
@Override
public void onNext(Result.RowColumn column) {
names.add(column.at("ename").get(String.class));
if (--demand < 1) {
subscription.request(10);
demand += 10;
}
}
@Override
public void onError(Throwable throwable) {
result.completeExceptionally(throwable);
}
@Override
public void onComplete() {
result.complete(names);
}
};
// Subscriber
continued

Row Publisher(continued)
return session.<List<String>>rowPublisherOperation(sql)
.subscribe(subscriber, result)
.submit();
}
} // fetchEmployees
28

Operation Submission Rate
public class RecordSubscriber implements Subscriber<byte[]> {
private final Session session;
private OperationGroup<Long, Long> group;
public RecordSubscriber(DataSource ds) {
session = ds.getSession();
}
@Override
public void onSubscribe(Subscription subscription) {
group = session.<Long, Long>operationGroup()
.independent()
.collect(Collectors.summingLong(c -> c));
group.submit();
session.requestHook(subscription::request);
}
continued
29

Operation Submission Rate (continued)
@Override
public void onNext(byte[] item) {
String insert = "insert into tab values (@record)";
group.<Long>rowCountOperation(insert)
.set("record", item, AdbaType.VARBINARY)
.apply(c -> c.getCount())
.submit();
}
@Override
public void onError(Throwable t) {
group.close();
session.close();
}
@Override
group.close();
session.close();
}
}
30

Controlling Session Creation Rate
public class ItemSubscriber implements Subscriber<Item> {
private final DataSourceFactory factory;
private DataSource ds;
public ItemSubscriber(DataSourceFactory f) {
factory = f;
}
@Override
public void onSubscribe(Subscription subscription) {
ds = factory.builder()
.url("//host.oracle.com:5521/example")
.username("scott")
.password("tiger")
.requestHook(subscription::request)
.build();
}
continued
31

Controlling Session Creation Rate (continued)
@Override
public void onNext(Item item) {
try (Session s = ds.getSession()) {
insertItem(s, item);
}
}
@Override
public void onError(Throwable t) {
ds.close();
}
@Override
ds.close();
}
}
32

Program Agenda
Introduction
Code
Wrap-up
Q&A
1
2
3
4
33

AoJ – ADBA over JDBC
• Proof-of-concept implementation that uses any standard JDBC driver
• Very limited functionality
• Source released under the Apache license
• Oracle is updating AoJ to track changes in ADBA
34

Status
• Everything is subject to change
• Developed through the Java Community Process
• You can participate via jdbc-spec-discuss@openjdk.java.net
• The API is available for download from OpenJDK at
http://hg.openjdk.java.net/jdk/sandbox/file/JDK-8188051-
branch/src/jdk.incubator.adba/share/classes
• AoJ source available at https://github.com/oracle/oracle-db-
examples/tree/master/java/AoJ
• Targeted for a near future release, Java 12 perhaps
35

Program Agenda
Introduction
Code
Wrap-up
Q&A
1
2
3
4
36

Q & A
37

Reactive Java Programming: A new Asynchronous Database Access API by Kuassi Mensah

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