### Overview With [Protocells](https://gitlab.com/groups/gitlab-com/gl-infra/-/epics/1616), we'll start to move towards multiple GitLab instances, each of which would have its database. When there are N cells, we will have N databases with potentially duplicated unique values across cells. Each cell cannot enforce true uniqueness if it doesn't know about other cells' databases. > [!important] > This is for tracking unique indexes to be addressed after the initial cohort because of low collision risk or the feature doesn't need to be supported initially ### Problem Current unique indexes may cause issues when: 1. Data needs to be transferred between cells - [Org Mover](https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/cells/migration/) 2. Global uniqueness is required but cannot be enforced locally (example: username, full path to the repo). ### Analysis As part of our analysis (from the database and the [uniqueness constraint in the application](https://guides.rubyonrails.org/active_record_validations.html#uniqueness)), we identified a total of 79 problematic Unique indexes. These indexes would cause issues if and when data needs to be moved from one cell to another. See the full report: DB constraint: https://docs.google.com/spreadsheets/d/1bhg3M7O05xholWeP7dkxp5o4Y1am4o4IgF03pdkIV6A/edit?gid=1766271401#gid=1766271401 Application: https://gitlab.com/gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team/-/issues/363#note_2680408090 [Topology Service ensures the clusterwide uniqueness](https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/cells/topology_service/#goals) for the claimed resources through the [`Claim Service`](https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/cells/topology_service/#claim-service)