[FF] ci_finished_builds_ch_sync_mode_split -- Split ClickHouse sync workers into recent/backfill modes

Summary

This issue is to roll out the feature on production, that is currently behind the ci_finished_builds_ch_sync_mode_split feature flag.

When enabled during backfill, it splits 5 sync workers into 2 "recent" workers (processing records from the last 7 days) and 3 "backfill" workers (processing older records), ensuring newer build data reaches ClickHouse faster.

Owners

  • Most appropriate Slack channel to reach out to: #g_ci-platform
  • Best individual to reach out to: @narendran-kannan

Expectations

What are we expecting to happen?

  • Recent builds (last 7 days) will be synced to ClickHouse with lower latency, as 2 dedicated workers process only recent records using ORDER BY build_finished_at ASC, build_id ASC with the new index
  • Backfill workers (3) continue processing older historical records independently
  • Overall throughput remains the same (5 total workers), but newer data is prioritized

What can go wrong and how would we detect it?

  • Sync lag could increase if the mode split causes workers to process fewer records overall. Monitor the ClickHouse sync lag dashboard.
  • The new order_by_build_finished_at keyset ordering could have unexpected behavior with the in-operator optimization. Detect via increased error rates on ClickHouse::CiFinishedBuildsSyncWorker.
  • If backfill workers fall behind, the backfill migration completion could be delayed. Monitor p_ci_finished_build_ch_sync_events table size.

Prerequisites

  • Index MR merged and deployed: !226067 (merged)
  • Verify index index_ci_finished_build_ch_sync_events_on_mode_filter exists in production
  • Code MR merged and deployed: !226068 (merged)

Rollout Steps

Note: Please make sure to run the chatops commands in the Slack channel that gets impacted by the command.

Rollout on non-production environments

  • Verify the MR with the feature flag is merged to master and has been deployed to non-production environments with /chatops run auto_deploy status <merge-commit-of-your-feature>
  • Enable the feature globally on non-production environments with /chatops run feature set ci_finished_builds_ch_sync_mode_split true --dev --pre --staging --staging-ref
  • Verify that the feature works as expected. The best environment to validate the feature in is staging-canary as this is the first environment deployed to. Make sure you are configured to use canary.
  • If the feature flag causes end-to-end tests to fail, disable the feature flag on staging to avoid blocking deployments.
    • See #e2e-run-staging Slack channel and look for the following messages:
      • test kicked off: Feature flag ci_finished_builds_ch_sync_mode_split has been set to true on **gstg**
      • test result: This pipeline was triggered due to toggling of ci_finished_builds_ch_sync_mode_split feature flag

If you encounter end-to-end test failures and are unable to diagnose them, you may reach out to the #s_developer_experience Slack channel for assistance. Note that end-to-end test failures on staging-ref don't block deployments.

Before production rollout

  • If the change is significant and you wanted to announce in #whats-happening-at-gitlab, it best to do it before rollout to gitlab-org/gitlab-com.

Specific rollout on production

For visibility, all /chatops commands that target production must be executed in the #production Slack channel and cross-posted (with the command results) to the responsible team's Slack channel.

  • Ensure that the feature MRs have been deployed to both production and canary with /chatops run auto_deploy status <merge-commit-of-your-feature>
  • Enable for all internal users: /chatops run feature set --feature-group=gitlab_team_members ci_finished_builds_ch_sync_mode_split true
  • Verify that the feature works for the specific actors.

Preparation before global rollout

  • Set a milestone to this rollout issue to signal for enabling and removing the feature flag when it is stable.
  • Check if the feature flag change needs to be accompanied with a change management issue. Cross link the issue here if it does.
  • Ensure that you or a representative in development can be available for at least 2 hours after feature flag updates in production. If a different developer will be covering, or an exception is needed, please inform the oncall SRE by using the @sre-oncall Slack alias.
  • Notify the #support_gitlab-com Slack channel and your team channel (more guidance when this is necessary in the dev docs).

Global rollout on production

For visibility, all /chatops commands that target production must be executed in the #production Slack channel and cross-posted (with the command results) to the responsible team's Slack channel.

Release the feature

After the feature has been deemed stable, the clean up should be done as soon as possible to permanently enable the feature and reduce complexity in the codebase.

You can either create a follow-up issue for Feature Flag Cleanup or use the checklist below in this same issue.

  • Create a merge request to remove the ci_finished_builds_ch_sync_mode_split feature flag. Ask for review/approval/merge as usual. The MR should include the following changes:
    • Remove all references to the feature flag from the codebase.
    • Remove the YAML definitions for the feature from the repository.
  • Ensure that the cleanup MR has been included in the release package. If the merge request was deployed before the monthly release was tagged, the feature can be officially announced in a release blog post: /chatops run release check <merge-request-url> <milestone>
  • Close the feature issue to indicate the feature will be released in the current milestone.
  • Once the cleanup MR has been deployed to production, clean up the feature flag from all environments by running these chatops command in #production channel: /chatops run feature delete ci_finished_builds_ch_sync_mode_split --dev --pre --staging --staging-ref --production
  • Close this rollout issue.

Rollback Steps

  • This feature can be disabled on production by running the following Chatops command:
/chatops run feature set ci_finished_builds_ch_sync_mode_split false
  • Disable the feature flag on non-production environments:
/chatops run feature set ci_finished_builds_ch_sync_mode_split false --dev --pre --staging --staging-ref
  • Delete feature flag from all environments:
/chatops run feature delete ci_finished_builds_ch_sync_mode_split --dev --pre --staging --staging-ref --production

Related

Edited by Narendran