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new a1791e95102f Revert "Revert "[improve][doc]Add introduction of
transaction isolation level in the txn-advanced-features.md (#712)""
a1791e95102f is described below
commit a1791e95102fda3470b8a9bcc01a4a2e6ac1ca4d
Author: visortelle <[email protected]>
AuthorDate: Mon May 27 12:44:20 2024 +0400
Revert "Revert "[improve][doc]Add introduction of transaction isolation
level in the txn-advanced-features.md (#712)""
This reverts commit 6ff9b3e10a3a65602ab60070ca4e3c40980a62bb.
---
docs/txn-advanced-features.md | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/docs/txn-advanced-features.md b/docs/txn-advanced-features.md
index 8819fcf8fba3..f00aa6f858c7 100644
--- a/docs/txn-advanced-features.md
+++ b/docs/txn-advanced-features.md
@@ -37,10 +37,33 @@ If you want to enable authentication with transactions,
follow the steps below.
2. [Configure authentication](security-overview/#authentication) in a Pulsar
client.
+## Select transaction isolation level
+
+To enhance the flexibility of Pulsar transactions, they support two distinct
isolation levels:
+- `READ_COMMITTED`(default): The consumer can only consume all transactional
messages that have been committed.
+- `READ_UNCOMMITTED`: The consumer can consume all messages, even
transactional messages that have been aborted.
+
+For different scenarios, they use different subscriptions and choose different
isolation levels. One scenario might require transactions, while another might
not. In general, not all subscriptions of the same topic require transaction
guarantees. Some want low latency without the exact-once semantic guarantee
(like a real-time monitoring system), and some must require the exactly-once
guarantee (e.g., business processing systems).
+Users can freely choose different isolation levels according to different
scenarios.
+
+Note that this is a subscription-level configuration, and all consumers under
the same subscription must be configured with the same isolation level.
+
+In this example, the consumer builder uses the `READ_UNCOMMITTED` isolation
level.
+
+```java
+Consumer<String> consumer = client
+ .newConsumer(Schema.STRING)
+ .topic("persistent://my-tenant/my-namespace/my-topic")
+ .subscriptionName("my-subscription")
+ .subscriptionType(SubscriptionType.Shared)
+ .subscriptionIsolationLevel(SubscriptionIsolationLevel.READ_UNCOMMITTED) //
Adding the isolation level configuration
+ .subscribe();
+```
+
## Guarantee exactly-once semantics
If you want to guarantee exactly-once semantics with transactions, you can
[enable message deduplication at the broker, namespace, or topic
level](cookbooks-deduplication.md#enable-message-deduplication-at-namespace-or-topic-level).
## Related topics
-- To get up quickly, see [Pulsar transactions - Get started](txn-use.md).
\ No newline at end of file
+- To get up quickly, see [Pulsar transactions - Get started](txn-use.md).
