Kafka Stream 中的 exactly once 处理配置是否保证只读取已提交的读取？
Does exactly once processing configuration in a Kafka Stream guarantee only read committed reads?
有一系列关于 Kafka 事务和 exactly once 传递的优秀文章。
In one of them作者对消费者的评价：
So on the Consumer side, you have two options for reading transactional messages, expressed through the “isolation.level” consumer config:
read_committed: In addition to reading messages that are not part of a transaction, also be able to read ones that are, after the
transaction is committed.
read_uncommitted: Read all messages in offset order without waiting for transactions to be committed. This option is similar to
the current semantics of a Kafka consumer.
也就是说，普通的消费者应用程序必须指定read_committed如果只想从主题中读取提交写入。
然而关于卡夫卡流：
All you need to make your Streams application employ exactly once
semantics, is to set this config “processing.guarantee=exactly_once”.
This causes all of the processing to happen exactly once; this
includes making both the processing and also all of the materialized
state created by the processing job that is written back to Kafka,
exactly once.
关于 KStream 中的读取没有明确说明。配置exactly_once后，KStream是否只读取提交的消息？
是的，KStream 只会读取已提交的消息，文档中没有明确说明，但在 StreamsConfig JavaDoc 中您会找到信息：
If "processing.guarantee" is set to "exactly_once", Kafka Streams does not allow users to overwrite the following properties (Streams setting shown in parentheses):
"isolation.level" (read_committed) - Consumers will always read committed data only
"enable.idempotence" (true) - Producer will always have idempotency enabled
"max.in.flight.requests.per.connection" (5) - Producer will always have one in-flight request per connection
有一系列关于 Kafka 事务和 exactly once 传递的优秀文章。
In one of them作者对消费者的评价：
So on the Consumer side, you have two options for reading transactional messages, expressed through the “isolation.level” consumer config:
read_committed: In addition to reading messages that are not part of a transaction, also be able to read ones that are, after the transaction is committed.
read_uncommitted: Read all messages in offset order without waiting for transactions to be committed. This option is similar to the current semantics of a Kafka consumer.
也就是说，普通的消费者应用程序必须指定read_committed如果只想从主题中读取提交写入。
然而关于卡夫卡流：
All you need to make your Streams application employ exactly once semantics, is to set this config “processing.guarantee=exactly_once”. This causes all of the processing to happen exactly once; this includes making both the processing and also all of the materialized state created by the processing job that is written back to Kafka, exactly once.
关于 KStream 中的读取没有明确说明。配置exactly_once后，KStream是否只读取提交的消息？
是的，KStream 只会读取已提交的消息，文档中没有明确说明，但在 StreamsConfig JavaDoc 中您会找到信息：
If "processing.guarantee" is set to "exactly_once", Kafka Streams does not allow users to overwrite the following properties (Streams setting shown in parentheses): "isolation.level" (read_committed) - Consumers will always read committed data only "enable.idempotence" (true) - Producer will always have idempotency enabled "max.in.flight.requests.per.connection" (5) - Producer will always have one in-flight request per connection