Enable leftover migration for Gitaly transaction

Production Change

Change Summary

The change is to enable Feature Flag gitaly_leftover_migration.

Some repositories may contain garbage files: files that are not part of the actual Git object store or refs. These can be created when Git temporary files are not cleaned up properly, or through manual operations that leave behind unexpected data. Since these files are not used by Gitaly, they add unnecessary overhead when creating repository snapshots.

Whether a file is considered “garbage” is determined by Gitaly’s snapshot filter. You can see the logic here.

The purpose of the leftover migration is to move all garbage files into a dedicated garbage folder:

<storage path>/+gitaly/leftover-migration-trash/

This migration only affects repositories hosted on nodes where the Gitaly transaction system is enabled. Repositories on nodes without transactions enabled will not be affected.

Also see gitlab-org/gitaly#6900 (closed)

Change Details

  1. Turn feature flag gitaly_leftover_migration to true
  2. If a repository has garbage, the garbage files would be moved to <storage path>/+gitaly/leftover-migration-trash/<repo path>. Otherwise, the repo is unaffected.
  3. Recovery instructions see gitlab-org/gitaly#6900 (closed)
  1. Services Impacted - Gitaly
  2. Change Technician - @eric.p.ju
  3. Change Reviewer - @msmiley
  4. Scheduled Date and Time (UTC in format 2025-11-21 17:30)
  5. Time tracking - 2 days
  6. Downtime Component - N/A

Important

If your change involves scheduled maintenance, add a step to set and unset maintenance mode per our runbooks. This will make sure SLA calculations adjust for the maintenance period.

Preparation

Note

The following checklists must be done in advance, before setting the label changescheduled

Change Reviewer checklist

C4 C3 C2 C1:

  • Check if the following applies:
    • The scheduled day and time of execution of the change is appropriate.
    • The change plan is technically accurate.
    • The change plan includes estimated timing values based on previous testing.
    • The change plan includes a viable rollback plan.
    • The specified metrics/monitoring dashboards provide sufficient visibility for the change.

C2 C1:

  • Check if the following applies:
    • The complexity of the plan is appropriate for the corresponding risk of the change. (i.e. the plan contains clear details).
    • The change plan includes success measures for all steps/milestones during the execution.
    • The change adequately minimizes risk within the environment/service.
    • The performance implications of executing the change are well-understood and documented.
    • The specified metrics/monitoring dashboards provide sufficient visibility for the change.
      • If not, is it possible (or necessary) to make changes to observability platforms for added visibility?
    • The change has a primary and secondary SRE with knowledge of the details available during the change window.
    • The change window has been agreed with Release Managers in advance of the change. If the change is planned for APAC hours, this issue has an agreed pre-change approval.
    • The labels blocks deployments and/or blocks feature-flags are applied as necessary.

Change Technician checklist

  • The Change Criticality has been set appropriately and requirements have been reviewed.
  • The change plan is technically accurate.
  • The rollback plan is technically accurate and detailed enough to be executed by anyone with access.
  • This Change Issue is linked to the appropriate Issue and/or Epic
  • Change has been tested in staging and results noted in a comment on this issue.
  • A dry-run has been conducted and results noted in a comment on this issue.
  • The change execution window respects the Production Change Lock periods.
  • Once all boxes above are checked, mark the change request as scheduled: /label ~"change::scheduled"
  • For C1 and C2 change issues, the change event is added to the GitLab Production calendar by the change-scheduler bot. It is schedule to run every 2 hours.
  • For C1 change issues, a Senior Infrastructure Manager has provided approval with the manager_approved label on the issue.
  • For C2 change issues, an Infrastructure Manager provided approval with the manager_approved label on the issue.
  • For C1 and C2 changes, mention @gitlab-org/saas-platforms/inframanagers in this issue to provide visibility to all infrastructure managers.
  • For C1, C2, or blocks deployments change issues, confirm with Release managers that the change does not overlap or hinder any release process (In #production channel, mention @release-managers and this issue and await their acknowledgment.)

Detailed steps for the change

Pre-execution steps

Note

The following steps should be done right at the scheduled time of the change request. The preparation steps are listed below.

  • Make sure all tasks in Change Technician checklist are done
  • For C1 and C2 change issues, the SRE on-call has been informed prior to change being rolled out. (Check the incident.io GitLab.com Production EOC schedule to find who will be on-call at the scheduled day and time. SREs on-call must be informed of plannable C1 changes at least 2 weeks in advance.)
    • The SRE on-call provided approval with the eoc_approved label on the issue.
  • For C1, C2, or blocks deployments change issues, Release managers have been informed prior to change being rolled out. (In #production channel, mention @release-managers and this issue and await their acknowledgment.)
  • There are currently no active incidents that are severity1 or severity2
  • If the change involves doing maintenance on a database host, an appropriate silence targeting the host(s) should be added for the duration of the change.

Change steps - steps to take to execute the change

Estimated Time to Complete (mins): 60 mins

  • Set label changein-progress /label ~change::in-progress

  • Find a few repositories who contains garbage files and turn on gitaly_leftover_migration for them:

    • The chosen repo is gitlab-org/production-engineering/runners-platform/gitlab-org-forks/gitlab, repoPaht is @hashed/6c/61/6c61d9ffdcbfe6a87461db9ddd0a14a70439c7ce0b877943e64dee7fe4719890.git.
    • The command is /chatops run feature set --project=gitlab-org/production-engineering/runners-platform/gitlab-org-forks/gitlab gitaly_leftover_migration true
    • The files expected to move: pack-4e9d82c6af8545f8739f0405f048941e37b0f0f8.mtimes

  • turn on gitaly_leftover_migration for Gitlab-org

    • The command is /chatops run feature set --group=gitlab-org gitaly_leftover_migration true

  • turn on gitaly_leftover_migration for all nodes.

  • Set label changecomplete /label ~change::complete

Rollback

Rollback steps - steps to be taken in the event of a need to rollback this change

Estimated Time to Complete (mins) - 1~5 mins for a repo (depending on the file numbers)

  • Locate the repository that need to recover
  • mv <storage path>/+gitaly/leftover-migration-trash/<repo path> <storage path>/<repo path>
  • Set label changeaborted /label ~change::aborted

Monitoring

Key metrics to observe

  • Metric: gitaly Service Error Ratio for CNY
Edited by Matt Smiley