Starting today, there is a simpler, more useful way to save and replay messages that are published to Pub/Sub: topic retention. Prior to topic retention, you needed to individually configure and pay for message retention in each subscription. Now, when you enable topic retention, all messages sent to the topic within the chosen retention window are accessible to all the topic’s subscriptions, without increasing your storage costs when you add subscriptions. Additionally, messages will be retained and available for replay even if there are no subscriptions attached to the topic at the time the messages are published.
Topic retention extends Pub/Sub’s existing seek functionality—message replay is no longer constrained to the subscription’s acknowledged messages. You can initialize new subscriptions with data retained by the topic, and any subscription can replay previously published messages. This makes it safer than ever to update stream processing code without fear of data processing errors, or to deploy new AI models and services built on a history of messages.
Topic retention explained
With topic retention, the topic is responsible for storing messages, independently of subscription retention settings. The topic owner has full control over the topic retention duration and pays the full cost associated with message storage by the topic. As a subscription owner, you can still configure subscription retention policies to meet your individual needs.
Initializing data for new use cases
As organizations become more mature at using streaming data, they often want to apply new use cases to existing data streams that they’ve published to Pub/Sub topics. With topic retention, you can access the history of this data stream for new use cases by creating a new subscription and seeking back to a desired point in time.
Using the GCloud CLI
These two commands initialize a new subscription and replay data from two days in the past. Retained messages are available within a minute after the seek operation is performed.
Choosing the retention option that’s right for you
Pub/Sub lets you choose between several different retention policies for your messages; here’s an overview of how we recommend you should use each type.
Topic retention lets you pay just once for all attached subscriptions, regardless of when they were created, to replay all messages published within the retention window. We recommend topic retention in circumstances where it is desirable for the topic owner to manage shared storage.
Subscription retention allows subscription owners, in a multi-tenant configuration, to guarantee their retention needs independently of the retention settings configured by the topic owner.
Snapshots are best used to capture the state of a subscription at the time of an important event, e.g. an update to subscriber code when reading from the subscription.
Transitioning from subscription retention to topic retention
You can configure topic retention when creating a new topic or updating an existing topic via the Cloud Console or the gcloud CLI. In the CLI, the command would look like:
gcloud pubsub topics update myTopic –message-retention-duration 7d.
If you are migrating to topic retention from subscription storage, subscription storage can be safely disabled after 7 days.
Pub/Sub topic retention makes reprocessing data with Pub/Sub simpler and more useful. To get started, you can read more about the feature, visit the pricing documentation, or simply enable topic retention on a topic using Cloud Console or the gcloud CLI.
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