Document bug in Reactive Extensions of the Oracle JDBC driver

See quarkusio#35477

docs/src/main/asciidoc/datasource.adoc

@@ -301,6 +301,22 @@ Quarkus offers several reactive clients for use with a reactive datasource.
 +
 The installed extension must be consistent with the `quarkus.datasource.db-kind` you define in your datasource configuration.
 
+[WARNING]
+====
+The Reactive Oracle datasource depends on the https://docs.oracle.com/en/database/oracle/oracle-database/23/jjdbc/jdbc-reactive-extensions.html[Reactive Extensions] provided by Oracle in its JDBC driver.
+
+There is a bug in versions 23.2 and 21.11 of the Oracle JDBC driver that prevents from getting any response if:
+
+* Reactive Extensions are used to execute an update/insert query that ends with an error (e.g. constraint violation), and
+* https://vertx.io/docs/vertx-oracle-client/java/#_retrieving_generated_key_values[generated keys retrieval] is enabled.
+
+It is not known yet when the bug will be fixed.
+In the meantime, you can either:
+
+* change the version of the driver in your project to `com.oracle.database.jdbc:ojdbc11:21.10.0.0`, or
+* avoid executing queries with generated keys retrieval (e.g. load sequence value before inserting)
+====
+
 . After adding the driver, configure the connection URL and define a proper size for your connection pool.
 +
 [source,properties]
@@ -318,7 +334,6 @@ Be aware that setting the pool size too low might cause some requests to time ou
 
 For more information about pool size adjustment properties, see the <<reactive-configuration>> section.
 
-
 ==== JDBC and reactive datasources simultaneously
 
 When a JDBC extension - along with Agroal - and a reactive datasource extension handling the given database kind are included, they will both be created by default.