# Unacknowledged Message Backlog in Abandoned Pub/Sub Subscriptions Canonical: https://www.pointfive.co/efficiency-hub/inefficiencies/unacknowledged-message-backlog-in-abandoned-pub-sub-subscriptions Every Pub/Sub subscription attached to a topic keeps its own backlog of the messages published to that topic until they are acknowledged or expire. By: PointFive Updated: 2026-09-28 [Cloud Efficiency Hub](https://www.pointfive.co/efficiency-hub) The short version Every Pub/Sub subscription attached to a topic keeps its own backlog of the messages published to that topic until they are acknowledged or expire. PointFive Research Cloud cost research at PointFive GCP service [GCP Pub/Sub](https://www.pointfive.co/efficiency-hub/cloud-services/gcp-pub-sub) Category [Other](https://www.pointfive.co/efficiency-hub/service-category/other) Reference CER-0492 Type Idle or Unused Resource ## Explanation Why the waste happens and who it affects. When a consumer is retired, broken or scaled too small, its subscription keeps receiving every new message, and unacknowledged messages older than one day start accruing message storage charges for as long as the subscription's retention duration allows. Test consumers, replaced services, one-off debugging subscriptions and pipelines migrated elsewhere commonly leave a subscription behind. Pub/Sub deletes inactive subscriptions after 31 days by default, but subscriptions set to never expire, or kept alive by a client that connects without acknowledging, persist indefinitely. Retaining acknowledged messages and long-lived snapshots add further storage on top of the backlog. ## Billing model The pricing dimensions that drive this cost. Pub/Sub bills throughput, data transfer and message storage. Unacknowledged backlog storage Charged per GiB-month for unacknowledged messages older than one day when the subscription's message retention duration is over one day, unless the topic already retains them Retained acknowledged messages Billed as message storage to the subscription's project when retain acknowledged messages is enabled Snapshots Billed for the messages they retain, plus a one-time fee equal to storing any existing backlog for seven days Message retention duration Defaults to 7 days for unacknowledged messages and can be set up to 31 days ## How to detect 5 checks to find it in your estate. - Chart subscription/oldest\_unacked\_message\_age\_by\_region and subscription/num\_unacked\_messages\_by\_region in Cloud Monitoring and flag subscriptions whose oldest unacknowledged message is consistently older than 24 hours - Cross-check activity with subscription/ack\_message\_count, subscription/pull\_request\_count and subscription/sent\_message\_count; a growing backlog with no acknowledgements means no working consumer - List subscriptions whose expiration policy is set to never expire and that have no identifiable owner or consumer - Find subscriptions with retain acknowledged messages enabled, and snapshots, that are not used for replay - Review the Pub/Sub message storage SKU in the Cloud Billing report by project to find where backlog storage is being billed ## How to fix 6 ways to remove the waste. - Delete subscriptions that have no active consumer after confirming with the owner; deleting the subscription removes its backlog and its storage charges - Fix or scale consumers so messages are acknowledged within 24 hours, which keeps backlog out of billable storage - For subscriptions that do not need replay, set the message retention duration to 1 day or less; backlog storage is charged only when the subscription's retention duration is over 1 day - Where replay is the real requirement, use topic message retention instead of per-subscription retention; Google describes it as the least expensive storage mechanism because one copy serves all attached subscriptions - Keep the default 31-day expiration policy on subscriptions unless a documented reason requires never expire, so abandoned subscriptions are cleaned up automatically - Disable retain acknowledged messages and delete snapshots that are no longer needed ## Documentation Vendor references for pricing and configuration. - [Pub/Sub pricing cloud.google.com](https://cloud.google.com/pubsub/pricing) - [Subscription properties docs.cloud.google.com](https://docs.cloud.google.com/pubsub/docs/subscription-properties) - [Configure message retention for a subscription docs.cloud.google.com](https://docs.cloud.google.com/pubsub/docs/subscription-message-retention) - [Monitor Pub/Sub in Cloud Monitoring docs.cloud.google.com](https://docs.cloud.google.com/pubsub/docs/monitoring) ## Related inefficiencies [Browse the library](https://www.pointfive.co/efficiency-hub) - GCP Cloud Logging CER-0262 ### [Suboptimal Storage for Logs](https://www.pointfive.co/efficiency-hub/inefficiencies/suboptimal-storage-for-logs-fd1d9) Many organizations retain all logs in Cloud Logging's standard storage, even when the data is rarely queried or required only for audit or compliance. Log bucket cost comes mainly from the per-GiB storage charge applied when logs are... Other - GCP Cloud Logging CER-0253 ### [Resources Generating Excessive INFO Logs](https://www.pointfive.co/efficiency-hub/inefficiencies/resources-generating-excessive-info-logs-6c920) Some GCP services and workloads generate INFO-level logs at very high frequencies - for example, load balancers logging every HTTP request or GKE nodes logging system health messages. While valuable for debugging, these logs can flood... Other - GCP Cloud Logging CER-0245 ### [Logging Buckets in Non-Production Environments Storing Info Logs](https://www.pointfive.co/efficiency-hub/inefficiencies/logging-buckets-in-non-production-environments-storing-info-logs-1edcf) Non-production environments frequently generate INFO-level logs that capture expected system behavior or routine API calls. While useful for troubleshooting in development, they rarely need to be retained. Allowing all INFO logs to be... Other --- Source: the public page above. Product screenshots and illustrative interfaces are examples, not live customer data.