[Feature flag] Enable `use_sql_functions_for_primary_key_lookups`
Summary
This issue is to roll out using SQL functions for PK lookup on production,
that is currently behind the use_sql_functions_for_primary_key_lookups
feature flag.
Owners
- Most appropriate Slack channel to reach out to:
#g_database
- Best individual to reach out to:
@krasio
@stomlinson
Expectations
What are we expecting to happen?
Minimize LockManager LWLock acquisitions, by replacing some of the most often executed queries with SQL function calls.
The queries we target are:
- {queryid="871736825776721136"}:
SELECT ... FROM "namespaces" WHERE "namespaces"."id" = $1 LIMIT 1
- {queryid="-338881497015521348"}:
SELECT ... FROM "projects" WHERE "projects"."id" = $1 LIMIT 1
- {queryid="517731457016766150"}:
SELECT ... FROM "users" WHERE "users"."id" = $1 LIMIT 1
These will be replaced with a query like
SELECT ... FROM find_{table}_by_id(35) "{table}" WHERE ("{table}"."id" IS NOT NULL) LIMIT 1
Once the feature flag is enabled, the execution rate for these queries should drop (link). During the first rollout to staging the drop was not as big as we expected though, see !135196 (comment 1640294637).
We should also see a drop in LWLock
events, although this may not be visible on the chart:
What can go wrong and how would we detect it?
We can monitor the following metrics:
Any spike in one of these may indicate that something is wrong and we need to. disable the feature flag. The more general PostgreSQL Overview dashboard is also worth checking.
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 have been deployed to non-production environments with/chatops run auto_deploy status <merge-commit-of-your-feature>
-
Deploy the feature flag at a percentage (recommended percentage: 50%) with /chatops run feature set <feature-flag-name> <rollout-percentage> --actors --dev --staging --staging-ref
-
Monitor that the error rates did not increase (repeat with a different percentage as necessary).
-
Enable the feature globally on non-production environments with /chatops run feature set use_sql_functions_for_primary_key_lookups true --dev --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.
For assistance with end-to-end test failures, please reach out via the #quality
Slack channel. Note that end-to-end test failures on staging-ref
don't block deployments.
Specific rollout on production
For visibility, all /chatops
commands that target production should 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>
-
Depending on the type of actor you are using, pick one of these options: - For project-actor:
/chatops run feature set --project=gitlab-org/gitlab,gitlab-org/gitlab-foss,gitlab-com/www-gitlab-com <feature-flag-name> true
- For group-actor:
/chatops run feature set --group=gitlab-org,gitlab-com <feature-flag-name> true
- For user-actor:
/chatops run feature set --user=<your-username> <feature-flag-name> true
- For project-actor:
-
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. -
Ensure that documentation has been updated. -
Leave a comment on the feature issue announcing estimated time when this feature flag will be enabled on GitLab.com. -
Ensure that any breaking changes have been announced following the release post process to ensure GitLab customers are aware. -
Notify the #support_gitlab-com
Slack channel and your team channel (more guidance when this is necessary in the dev docs). -
Ensure that the feature flag rollout plan is reviewed by another developer familiar with the domain.
Global rollout on production
For visibility, all /chatops
commands that target production should be executed in the #production
Slack channel
and cross-posted (with the command results) to the responsible team's Slack channel (#g_TEAM_NAME
).
-
(Optional) Incrementally roll out the feature on production environment. - Between every step wait for at least 15 minutes and monitor the appropriate graphs on https://dashboards.gitlab.net.
-
Perform actor-based rollout: -
/chatops run feature set use_sql_functions_for_primary_key_lookups 0.1 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 0.5 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 1 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 5 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 10 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 25 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 50 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 75 --actors
-
/chatops run feature set use_sql_functions_for_primary_key_lookups 100 --actors
-
-
Enable the feature globally on production environment: /chatops run feature set use_sql_functions_for_primary_key_lookups true
-
Observe appropriate graphs on https://dashboards.gitlab.net and verify that services are not affected. -
Leave a comment on the feature issue announcing that the feature has been globally enabled. -
Wait for at least one day for the verification term.
(Optional) Release the feature with the feature flag
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.
See instructions if you're sure about enabling the feature globally through the feature flag definition
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
. -
Decide which changelog entry is needed.
-
-
Ensure that the default-enabling 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>
-
Consider cleaning up the feature flag from all environments by running these chatops command in #production
channel. Otherwise these settings may override the default enabled:/chatops run feature delete use_sql_functions_for_primary_key_lookups --dev --staging --staging-ref --production
-
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 use_sql_functions_for_primary_key_lookups
". -
Execute the /copy_metadata https://gitlab.com/gitlab-org/gitlab/-/issues/429479
quick action to copy the labels from this rollout issue. -
Link this rollout issue as a related issue. -
Close this rollout issue.
-
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 use_sql_functions_for_primary_key_lookups
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.
- Create a changelog entry.
-
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. -
Clean up the feature flag from all environments by running these chatops command in #production
channel:/chatops run feature delete use_sql_functions_for_primary_key_lookups --dev --ops --pre --staging --staging-ref --production
-
Close this rollout issue.
Rollback Steps
-
This feature can be disabled by running the following Chatops command:
/chatops run feature set use_sql_functions_for_primary_key_lookups false