SpringOne 2021 Session Title:The Making of the Oracle R2DBC Driver and How to Take Your Code from Synchronous to Reactive Speakers: Kuassi Mensah, Director of Product Management at Oracle; Michael McMahon, Principal Member of Technical Staff at Oracle

1. The Making of the Oracle R2DBC Driver
And How to Take Your Code from Synchronous to Reactive
Kuassi Mensah Michael McMahon
@kmensah

2. Agenda
ü Once Upon a Time
• The Making of Oracle R2DBC driver
• Taking Your Code from Synchronous to Reactive
Oracle Confidential

3. Once Upon a Time …
The Asynchronous Database Access API (ADBA)
• Started in 2017
• Goal
– A standard Java database access API that never blocks user threads
– No compatibility or complementarity with JDBC
• Motivations
– Asynchronous apps have better throughput
– Simultaneous access to multiple databases, e.g. map/reduce, sharded databases
– Fire and forget, e.g. DML, stored procedures
• The API is available from OpenJDK at https://bit.ly/3t3nkAd
3

4. 1. Per the Java SE team: “the future of Java scalability is Virtual
Threads”
–ADBA would not be accepted as a Java standard as it was an
async solution to a problem that would be addressed by virtual
threads.
– Unless it became a standard ADBA would have very little
impact, certainly not enough to justify the effort.
2. There was very little support within the Java community.
-- Gravitating towards R2DBC
4
Why Did We Stop Working on ADBA?

5. We changed our focus towards
• JDBC Reactive Extensions
• An Oracle R2DBC Driver
• Instrumenting the JDBC driver to support Virtual Threads
5
Then What?

6. SQL Execution (OraclePreparedStatement):
Publisher<Boolean> executeAsyncOracle()
Publisher<Long> executeUpdateAsyncOracle()
Publisher<Long> executeBatchAsyncOracle()
Publisher<OracleResultSet> executeQueryAsyncOracle()
Row Fetching (OracleResultSet):
Publisher<T> publisherOracle(Function<OracleRow, T> f)
LOB I/O (OracleBlob):
Publisher<byte[]> publisherOracle(long position)
Subscriber<byte[]> subscriberOracle(long position)
LOB I/O (OracleClob):
Publisher<String> publisherOracle(long position)
Subscriber<String> subscriberOracle(long position)
Connection Closing (OracleConnection):
Publisher<Success> closeAsyncOracle()
Transaction Closing (OracleConnection):
Publisher<Success> commitAsyncOracle()
Publisher<Success> rollbackAsyncOracle()
Connection Creation (OracleConnectionBuilder):
Publisher<OracleConnection> buildConnectionPublisherOracle()
JDBC Reactive Extensions (built into the driver)

7. User
Java
Code
JDBC
Reactive
Extension Standard
JDBC
API
3rd party
Reactive
Streams
Libraries
Async call with non-blocking
backpressure
operators (map, reduce, filters),
concurrency modeling,
monitoring, tracing
Implements Java SE
reactive stream
interface (Flow)
Full Reactive
Streams
Sync/blocking JDBC calls
Java
Business
Logic
User Java code
Oracle
Database
Oracle JDBC
driver
Summary of Oracle DB Access with Java – Part 1

8. Agenda
• Once Upon a Time
ü The Making of Oracle R2DBC driver
• Taking Your Code from Synchronous to Reactive
Oracle Confidential

9. public boolean execute() throws SQLException {
// Check if this statement is closed
if (isClosed)
throw new SQLException("Closed Statement");
// Check if all bind values are set
for (Object bindValue : bindValues) {
if (bindValue == null)
throw new SQLException("Bind value not set");
}
// Close the current ResultSet
if (resultSet != null)
resultSet.close();
// Reset the current update count
updateCount = -1;
// Blocking database call
SqlResult sqlResult = jdbcConnection.executeSql(sql, bindValues);
// Handle the result
resultSet = sqlResult.getResultSet();
updateCount = sqlResult.getUpdateCount();
return resultSet != null;
}
public Publisher<Boolean> executeAsyncOracle() throws SQLException {
// Check if this statement is closed
if (isClosed)
throw new SQLException("Closed Statement");
// Check if all bind values are set
for (Object bindValue : bindValues) {
if (bindValue == null)
throw new SQLException("Bind value not set");
}
// Close the current ResultSet
if (resultSet != null)
resultSet.close();
// Reset the current update count
updateCount = -1;
// Non-blocking database call
return Flux.from(jdbcConnection.executeSqlAsync(sql, bindValues))
.map(sqlResult -> {
// Handle the result
resultSet = sqlResult.getResultSet();
updateCount = sqlResult.getUpdateCount();
return resultSet != null;
});
}
Developing JDBC Reactive Extensions

10. public boolean execute() throws SQLException {
// Check if this statement is closed
if (isClosed)
throw new SQLException("Closed Statement");
// Check if all bind values are set
for (Object bindValue : bindValues) {
if (bindValue == null)
throw new SQLException("Bind value not set");
}
// Close the current ResultSet
if (resultSet != null)
resultSet.close();
// Reset the current update count
updateCount = -1;
// Blocking database call
SqlResult sqlResult = jdbcConnection.executeSql(sql, bindValues);
// Handle the result
resultSet = sqlResult.getResultSet();
updateCount = sqlResult.getUpdateCount();
return resultSet != null;
}
public Publisher<Boolean> executeAsyncOracle() throws SQLException {
// Check if this statement is closed
if (isClosed)
throw new SQLException("Closed Statement");
// Check if all bind values are set
for (Object bindValue : bindValues) {
if (bindValue == null)
throw new SQLException("Bind value not set");
}
// Close the current ResultSet
if (resultSet != null)
resultSet.close();
// Reset the current update count
updateCount = -1;
// Non-blocking database call
return Flux.from(jdbcConnection.executeSqlAsync(sql, bindValues))
.map(sqlResult -> {
// Handle the result
resultSet = sqlResult.getResultSet();
updateCount = sqlResult.getUpdateCount();
return resultSet != null;
});
}
Developing JDBC Reactive Extensions

11. public boolean execute() throws SQLException {
prepareForExecute();
SqlResult result = jdbcConnection.executeSql(sql, bindValues);
return handleResult(result);
}
public Publisher<Boolean> executeAsyncOracle() throws SQLException {
prepareForExecute();
return Flux.from(jdbcConnection.executeSqlAsync(sql, bindValues))
.map(sqlResult -> handleResult(sqlResult));
}
private void prepareForExecute() throws SQLException {
// Check if this statement is closed
if (isClosed)
throw new SQLException("Closed Statement");
// Check if all bind values are set
for (Object bindValue : bindValues) {
if (bindValue == null)
throw new SQLException("Bind value not set");
}
// Close the current ResultSet
if (resultSet != null)
resultSet.close();
// Reset the current update count
updateCount = -1;
}
private boolean handleResult(SqlResult result) {
resultSet = result.getResultSet();
updateCount = result.getUpdateCount();
return resultSet != null;
}
Developing JDBC Reactive Extensions

12. Developing JDBC Reactive Extensions
Setup
Blocking
Handle Result
Setup
Non-Blocking
Handle Result
Synchronous JDBC Setup
Blocking
Handle Result
Setup
Non-Blocking
Handle Result
Setup
Non-Blocking
Handle Result
Reactive JDBC
Database
Setup
Blocking
Handle Result
Database

13. Adapting JDBC Reactive Extensions for Oracle
R2DBC
R2DBC SPI Reactive Extensions API
ConnectionFactory
create()
OracleConnectionBuilder
buildConnectionPublisherOracle()
Statement
execute()
OraclePreparedStatement
executeAsyncOracle()
Result
map(Function)
OracleResultSet
publisherOracle(Function)
https://github.com/oracle/oracle-r2dbc

14. Adapting JDBC Reactive Extensions for Oracle
R2DBC
R2DBC SPI Reactive Extensions API
Connection
commit()
OracleConnection
commitAsyncOracle()
Blob
stream()
OracleBlob
publisherOracle()
Clob
stream()
OracleClob
publisherOracle()
rollback()
close()
rollbackAsyncOracle()
closeAsyncOracle()
https://github.com/oracle/oracle-r2dbc

15. Agenda
• Once Upon a Time
• The Making of Oracle R2DBC driver
ü Taking Your Code from Synchronous to Reactive
Oracle Confidential

16. From Synchronous to Reactive: Configuration
static DataSource configureJdbc() throws SQLException {
OracleDataSource dataSource = new oracle.jdbc.pool.OracleDataSource();
dataSource.setDriverType("thin");
dataSource.setServerName(DatabaseConfig.HOST);
dataSource.setPortNumber(DatabaseConfig.PORT);
dataSource.setServiceName(DatabaseConfig.SERVICE_NAME);
dataSource.setUser(DatabaseConfig.USER);
dataSource.setPassword(DatabaseConfig.PASSWORD);
return dataSource;
}
static ConnectionFactory configureR2dbc() {
return ConnectionFactories.get(ConnectionFactoryOptions.builder()
.option(DRIVER, "oracle")
.option(HOST, DatabaseConfig.HOST)
.option(PORT, DatabaseConfig.PORT)
.option(DATABASE, DatabaseConfig.SERVICE_NAME)
.option(USER, DatabaseConfig.USER)
.option(PASSWORD, DatabaseConfig.PASSWORD)
.build());
}

17. From Synchronous to Reactive: Query
static String queryJdbc(java.sql.Connection connection) throws SQLException {
try (java.sql.Statement statement = connection.createStatement()) {
ResultSet resultSet =
statement.executeQuery("SELECT 'Hello, JDBC!' FROM sys.dual");
if (resultSet.next())
return resultSet.getString(1);
else
throw new NoSuchElementException("Query returned zero rows");
}
}
static Publisher<String> queryR2dbc(io.r2dbc.spi.Connection connection) {
return Flux.from(connection.createStatement(
"SELECT 'Hello, R2DBC!' FROM sys.dual")
.execute())
.flatMap(result ->
result.map(row -> row.get(0, String.class)))
.switchIfEmpty(Flux.error(
new NoSuchElementException("Query returned zero rows")));
}
Flat Map:
f(x) -> { y0, y1, …, yn }
{ x0, x1, …, xn } -> { f(x0), f(x1), … f(xn)}
{ y0-0, y0-1, …, y0-n, y1-0, y1-1, …, y1-n, …, yn-n}

18. From Synchronous to Reactive: Insert
static int insertJdbc(java.sql.Connection connection) throws SQLException {
try (PreparedStatement preparedStatement = connection.prepareStatement(
"INSERT INTO JdbcToR2dbcTable(id, value) VALUES (?, ?)")) {
preparedStatement.setInt(1, 0);
preparedStatement.setString(2, "JDBC");
return preparedStatement.executeUpdate();
}
}
static Publisher<Integer> insertR2dbc(io.r2dbc.spi.Connection connection) {
return Flux.from(connection.createStatement(
"INSERT INTO JdbcToR2dbcTable(id, value) VALUES (?, ?)")
.bind(0, 0)
.bind(1, "R2DBC")
.execute())
.flatMap(Result::getRowsUpdated);
}

19. From Synchronous to Reactive: Update
static int updateJdbc(java.sql.Connection connection) throws SQLException {
try (PreparedStatement preparedStatement = connection.prepareStatement(
"UPDATE JdbcToR2dbcTable SET value = ? WHERE id = ?")) {
preparedStatement.setString(1, "JDBC");
preparedStatement.setInt(2, 0);
return preparedStatement.executeUpdate();
}
}
static Publisher<Integer> updateR2dbc(io.r2dbc.spi.Connection connection) {
return Flux.from(connection.createStatement(
"UPDATE JdbcToR2dbcTable SET value = ? WHERE id = ?")
.bind(0, "R2DBC")
.bind(1, 0)
.execute())
.flatMap(Result::getRowsUpdated);
}

20. From Synchronous to Reactive: Conditional
Branch
static int tryUpdateJdbc(java.sql.Connection connection) throws SQLException
{
// Try to update the row
int updateCount = updateJdbc(connection);
// If the row does not exist, then insert it.
if (updateCount == 0)
return insertJdbc(connection);
else
return updateCount;
}
static Publisher<Integer> tryUpdateR2dbc(io.r2dbc.spi.Connection connection)
{
// Try to update the row
return Flux.from(updateR2dbc(connection))
.flatMap(updateCount -> {
// If the row does not exist, then insert it.
if (updateCount == 0)
return insertR2dbc(connection);
else
return Flux.just(updateCount);
});
}

21. From Synchronous to Reactive: Error Recovery
static int tryInsertJdbc(java.sql.Connection connection) throws SQLException
{
try {
// Try to insert the row
return insertJdbc(connection);
}
catch (SQLException sqlException) {
// If the row already exists, then update it.
if (sqlException.getErrorCode() == UNIQUE_CONSTRAINT_VIOLATION)
return updateJdbc(connection);
else
throw sqlException;
}
}
static Publisher<Integer> tryInsertR2dbc(io.r2dbc.spi.Connection connection)
{
// Try to insert the row
return Flux.from(insertR2dbc(connection))
.onErrorResume(R2dbcException.class, r2dbcException -> {
// If the row already exists, then update it.
if (r2dbcException.getErrorCode() == UNIQUE_CONSTRAINT_VIOLATION)
return updateR2dbc(connection);
else
return Flux.error(r2dbcException);
});
}

22. From Synchronous to Reactive: Loop
static int loopJdbc(java.sql.Connection connection) throws SQLException {
do {
try {
// Try to update the row, or insert it if it does not exist
return tryUpdateJdbc(connection);
}
catch (SQLException sqlException) {
// If another database session has inserted the row before this
// one did, then recover from failure by continuing the loop.
if (sqlException.getErrorCode() != UNIQUE_CONSTRAINT_VIOLATION)
throw sqlException;
}
} while (true);
}
static Publisher<Integer> loopR2dbc(io.r2dbc.spi.Connection connection) {
// Try to update the row, or insert it if it does not exist
return Flux.from(tryUpdateR2dbc(connection))
.onErrorResume(R2dbcException.class, r2dbcException -> {
// If another database session has inserted the row before this
// one did, then recover from failure by recursively invoking this
// method.
if (r2dbcException.getErrorCode() != UNIQUE_CONSTRAINT_VIOLATION)
return Flux.error(r2dbcException);
else
return loopR2dbc(connection);
});
}

23. User
Java
Code
JDBC
Reactive
Extension Standard
JDBC API
R2DBC
+
3rd party
Reactive
Streams
Libraries
Async call with non-blocking
backpressure
operators (map, reduce, filters),
concurrency modeling,
monitoring, tracing
Implements Java SE
reactive stream
interface (Flow)
Full Reactive
Streams
Sync/blocking JDBC calls
Java
Business
Logic
User Java code
Oracle
Database
Oracle JDBC
driver
Summary of Oracle DB Access with Java – Part 2