### Background During a [recent analysis](https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/2538) of memory usage in Redis Shared State, we discovered that [gitlab-experiment](https://gitlab.com/gitlab-org/ruby/gems/gitlab-experiment) was a large consumer of memory. ### Problem However, it was difficult to identify which keys exactly belong to the experiment framework, because they are not in any way namespaced or prefixed. We end up with rather generic key names like `logged_out_marketing_header` or `tier_badge`. In addition to the attribution challenge, this also creates a risk for collisions. ### Proposal As such it would be advisable to migrate these keys to have a `gitlab:experiment:` or `glex:` prefix, as it makes this kind of analysis much easier. Migration may need to support both namespaced and non-namespaced keys during the migration phase. ~"group::scalability" is able to advise and assist with the process if needed. To implement this prefix, we'll need to consider this as multiple steps: - [ ] Add the ability in gitlab-experiment gem to have a prefix [configured](https://gitlab.com/gitlab-org/ruby/gems/gitlab-experiment/-/blob/948bc7aa07ec95d46702b3e6b0ff26ebac2bda3f/lib/gitlab/experiment/configuration.rb#L28-28) in `config/initializers/gitlab_experiment.rb`. - this will likely mean modifying `lib/gitlab/experiment/cache/redis_hash_store.rb` and `lib/gitlab/experiment/cache.rb` and then implementing in GitLab initially with a `nil` value and then figure out a migration plan. - [ ] Migrate(or not) existing keys to new pattern. - maybe there aren't many experiments at the time of this finishing or all are at 100% or 0% values, so migration will not be required. This will need verified at time of implementation. - [ ] Change the configured value for GitLab in `config/initializers/gitlab_experiment.rb` to have the `glex` prefix. - This would likely need either done in a db migration on deployment(it would need to be sure it is executed at right time) or have some sort of deprecation period where things are automatically handled for a bit of time by saying 'if existing use this format, if not use new format' as a monkey patch in GitLab.