[Feature flag] Enable PG12 database reindexing
Summary
This issue is to rollout the PG12 database reindexing on production,
that is currently behind the database_reindexing_pg12
feature flag.
This changes behavior of reindexing to leverage PG12 feature REINDEX CONCURRENTLY
instead of doing this manually. With this, we start to support unique/primary key indexes for reindexing.
Background/MRs:
- Strategy adjustments for index selection: !65655 (merged)
- Support for unique indexes using
REINDEX
: !64695 (merged) - Background on current bloat state on .com: &3989 (comment 620730954)
Owners
- Team: groupdatabase
- Most appropriate slack channel to reach out to:
#g_database
- Best individual to reach out to: @abrandl
- PM: @fzimmer
Stakeholders
- SRE
The Rollout Plan - tbd
-
Tested in staging -
Enable for weekend reindexing on .com
Expectations
What are we expecting to happen?
Mostly unique indexes being picked up for reindexing
What might happen if this goes wrong?
- Long running index re-creation can cause elevated dead tuple rates and block autovacuum
- If we overlooked managing lock acquires properly, it can stall unrelated traffic
What can we monitor to detect problems with this?
- Patroni dashboards
Rollout Steps
Preparation before production rollout
-
Ensure that the feature MRs have been deployed to both production and canary. -
/chatops run auto_deploy status <merge-commit-of-your-feature>
-
-
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.
Global rollout on production
-
Incrementally roll out the feature. - If the feature flag in code has an actor, perform actor-based rollout.
-
/chatops run feature set <feature-flag-name> <rollout-percentage> --actors
-
- If the feature flag in code does NOT have an actor, perform time-based rollout (random rollout).
-
/chatops run feature set <feature-flag-name> <rollout-percentage>
-
- Enable the feature globally on production environment.
-
/chatops run feature set <feature-flag-name> true
-
- If the feature flag in code has an actor, perform actor-based rollout.
-
Announce on the feature issue that the feature has been globally enabled. -
Cross-post chatops slack command to #support_gitlab-com
. (more guidance when this is necessary in the dev docs) and in your team channel -
Wait for at least one day for the verification term.
(Optional) Release the feature with the feature flag
If you're still unsure whether the feature is deemed stable but want to release it in the current milestone, you can change the default state of the feature flag to be enabled. To do so, follow these steps:
-
Create a merge request with the following changes. Ask for review and merge it. -
Set the default_enabled
attribute in the feature flag definition totrue
. -
Create a changelog entry.
-
-
Ensure that the above MR has been deployed to both production and canary. If the merge request was deployed before the code cutoff, the feature can be officially announced in a release blog post. -
/chatops run auto_deploy status <merge-commit>
-
-
Close the feature issue to indicate the feature will be released in the current milestone. -
Set the next milestone to this rollout issue for scheduling the flag removal. -
(Optional) You can create a separate issue for scheduling the steps below to Release the feature. -
Set the title to "[Feature flag] Cleanup <feature-flag-name>
". -
Execute the /copy_metadata <this-rollout-issue-link>
quick action to copy the labels from this rollout issue. -
Link this rollout issue as a related issue. -
Close this rollout issue.
-
WARNING: This approach has the downside that it makes it difficult for us to clean up the flag. For example, on-premise users could disable the feature on their GitLab instance. But when you remove the flag at some point, they suddenly see the feature as enabled and they can't roll it back to the previous behavior. To avoid this potential breaking change, use this approach only for urgent matters.
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.
-
Create a merge request to remove <feature-flag-name>
feature flag. Ask for review and merge it.-
Remove all references to the feature flag from the codebase. -
Remove the YAML definitions for the feature from the repository. -
Create a changelog entry.
-
-
Ensure that the above MR has been deployed to both production and canary. If the merge request was deployed before the code cutoff, the feature can be officially announced in a release blog post. -
/chatops run auto_deploy status <merge-commit>
-
-
Close the feature issue to indicate the feature will be released in the current milestone. -
Clean up the feature flag from all environments by running these chatops command in #production
channel:-
/chatops run feature delete <feature-flag-name> --dev
-
/chatops run feature delete <feature-flag-name> --staging
-
/chatops run feature delete <feature-flag-name>
-
-
Close this rollout issue.
Rollback Steps
-
This feature can be disabled by running the following Chatops command:
/chatops run feature set database_reindexing_pg12 false