Transaction Doc Polishing

Author: garyrussell

src/reference/asciidoc/kafka.adoc

@@ -3194,19 +3194,20 @@ Instead, a new "nested" transaction is used.
 ===== `transactionIdPrefix`
 
 As mentioned in <<transactions, the overview>>, the producer factory is configured with this property to build the producer `transactional.id` property.
-There is rather a dichotomy when specifying this property in that, when running multiple instances of the application, it must be the same on all instances to satisfy fencing zombies (also mentioned in the overview) when producing records on a listener container thread.
+There is a dichotomy when specifying this property in that, when running multiple instances of the application with `EOSMode.ALPHA`, it must be the same on all instances to satisfy fencing zombies (also mentioned in the overview) when producing records on a listener container thread.
 However, when producing records using transactions that are **not** started by a listener container, the prefix has to be different on each instance.
 Version 2.3, makes this simpler to configure, especially in a Spring Boot application.
 In previous versions, you had to create two producer factories and `KafkaTemplate` s - one for producing records on a listener container thread and one for stand-alone transactions started by `kafkaTemplate.executeInTransaction()` or by a transaction interceptor on a `@Transactional` method.
 
 Now, you can override the factory's `transactionalIdPrefix` on the `KafkaTemplate` and the `KafkaTransactionManager`.
 
 When using a transaction manager and template for a listener container, you would normally leave this to default to the producer factory's property.
-This value should be the same for all application instances.
+This value should be the same for all application instances when using `EOSMode.ALPHA`.
+With `EOSMode.BETA` it is no longer necessary to use the same `transactional.id`, even for consumer-initiated transactions; in fact, it must be unique on each instance the same as producer-initiated transactions.
 For transactions started by the template (or the transaction manager for `@Transaction`) you should set the property on the template and transaction manager respectively.
 This property must have a different value on each application instance.
 
-This problem has been eliminated when `EOSMode.BETA` is being used (with broker versions >= 2.5); see <<exactly-once>>.
+This problem (different rules for `transactional.id`) has been eliminated when `EOSMode.BETA` is being used (with broker versions >= 2.5); see <<exactly-once>>.
 
 [[tx-template-mixed]]
 ===== `KafkaTemplate` Transactional and non-Transactional Publishing
@@ -3318,6 +3319,8 @@ You can then do a rolling upgrade of your application with `producerPerConsumerP
 
 If your brokers are already 2.5 or newer, you should set the `DefaultKafkaProducerFactory` `producerPerConsumerPartition` property to `false`, to reduce the number of producers needed.
 
+IMPORTANT: When using `EOSMode.BETA` with `producerPerConsumerPartition=false` the `transactional.id` must be unique across all application instances.
+
 When using `BETA` mode, it is no longer necessary to set the `subBatchPerPartition` to `true`; it will default to `false` when the `EOSMode` is `BETA`.
 
 Refer to https://cwiki.apache.org/confluence/display/KAFKA/KIP-447%3A+Producer+scalability+for+exactly+once+semantics[KIP-447] for more information.