> ## Documentation Index > Fetch the complete documentation index at: https://docs.internal.nscale.com/llms.txt > Use this file to discover all available pages before exploring further. # Reassign device rack slots atomically > Move devices to new rack slots as one unit, so they can cross over. The single-device update path cannot express a swap. `(rack, position)` is unique, so whichever of the two devices moves first lands on the other — there is no ordering that avoids it, and the netbox agent consequently deadlocked on every tray swap and served the pre-swap location indefinitely. This applies the whole batch in one transaction, with the constraint DEFERRED so it is judged once at COMMIT rather than per row. `QuerySet.update()` is used deliberately: `full_clean` would reject the intermediate overlap in Python before the database ever saw it (`BaseModel.validate_constraints` refuses to exclude fields, by design), so nothing outside the transaction observes the crossing. Bypassing `full_clean` means the invariants it would have applied are the serializer's job instead: it derives `location`/`site` from the target rack (they are non-editable and normally re-derived by `Device.save()`) and rejects a batch that no ordering could satisfy. Only those four columns are written — name, Ironic reference and status are untouched, because a physical move is all this represents. The occupancy check covers only `(rack, position)`, not NVSwitch slots. A bad NVSwitch slot swap therefore fails at commit with HTTP 409. NVSwitch rack moves are manual in the M1.5 milestone. Revisit this check before automating them in a later milestone. Every member is locked in device-id order before anything is written. Two agent workers reconciling the two halves of one swap concurrently each put their own device first, which would be a lock cycle and a Postgres deadlock; taking the locks in a stable order makes the loser wait instead, and it is then a no-op because the winner already committed the layout it was going to write. The same lock closes the window in which a member deleted after validation would leave its partner's move committed on its own — that returns 409 rather than a half-applied swap. ## OpenAPI ````yaml /openapi/fleet-manager-openapi.yaml post /api/v1/devices/reassign-slots/ openapi: 3.0.3 info: title: Fleet Manager API version: 1.0.0 description: API for the Nscale Fleet Manager servers: [] security: [] paths: /api/v1/devices/reassign-slots/: post: tags: - Devices summary: Reassign device rack slots atomically description: >- Move devices to new rack slots as one unit, so they can cross over. The single-device update path cannot express a swap. `(rack, position)` is unique, so whichever of the two devices moves first lands on the other — there is no ordering that avoids it, and the netbox agent consequently deadlocked on every tray swap and served the pre-swap location indefinitely. This applies the whole batch in one transaction, with the constraint DEFERRED so it is judged once at COMMIT rather than per row. `QuerySet.update()` is used deliberately: `full_clean` would reject the intermediate overlap in Python before the database ever saw it (`BaseModel.validate_constraints` refuses to exclude fields, by design), so nothing outside the transaction observes the crossing. Bypassing `full_clean` means the invariants it would have applied are the serializer's job instead: it derives `location`/`site` from the target rack (they are non-editable and normally re-derived by `Device.save()`) and rejects a batch that no ordering could satisfy. Only those four columns are written — name, Ironic reference and status are untouched, because a physical move is all this represents. The occupancy check covers only `(rack, position)`, not NVSwitch slots. A bad NVSwitch slot swap therefore fails at commit with HTTP 409. NVSwitch rack moves are manual in the M1.5 milestone. Revisit this check before automating them in a later milestone. Every member is locked in device-id order before anything is written. Two agent workers reconciling the two halves of one swap concurrently each put their own device first, which would be a lock cycle and a Postgres deadlock; taking the locks in a stable order makes the loser wait instead, and it is then a no-op because the winner already committed the layout it was going to write. The same lock closes the window in which a member deleted after validation would leave its partner's move committed on its own — that returns 409 rather than a half-applied swap. operationId: api_v1_devices_reassign_slots_create requestBody: content: application/json: schema: $ref: '#/components/schemas/DeviceReassignSlotsRequest' application/x-www-form-urlencoded: schema: $ref: '#/components/schemas/DeviceReassignSlotsRequest' multipart/form-data: schema: $ref: '#/components/schemas/DeviceReassignSlotsRequest' required: true responses: '200': content: application/json: schema: $ref: '#/components/schemas/DeviceReassignSlotsResponse' description: '' '400': description: Validation error. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '401': description: Authentication credentials were not provided or are invalid. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '403': description: You do not have permission to perform this action. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '409': description: >- The devices or rack positions changed while the reassignment was being applied; re-read the layout and retry. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - oauth2: - device:update - cookieAuth: [] components: schemas: DeviceReassignSlotsRequest: type: object description: >- Input payload for the atomic slot reassignment action. Every assignment is applied together, so a set that merely *passes through* an occupied slot — the swap case, where each device wants the other's — is legal even though no single assignment in it is. ``max_length`` documents the intent as much as it bounds the work: the netbox agent submits one 2-device swap, and each assignment costs its own UPDATE inside a single transaction holding row locks until COMMIT. properties: assignments: type: array items: $ref: '#/components/schemas/DeviceSlotAssignment' maxItems: 64 minItems: 1 required: - assignments DeviceReassignSlotsResponse: type: object description: Result of an atomic slot reassignment. properties: devices_changed: type: integer required: - devices_changed ErrorResponse: type: object description: >- Uniform error body for every 4xx/5xx response. `detail` is a human-readable message, always present, safe to display to end users. `code` is the machine-readable identifier. `field_errors` lists per-input-field validation messages and is empty for non-field errors (auth, permission, not-found, conflict, server). required: - detail - code - field_errors properties: detail: type: string code: $ref: '#/components/schemas/ErrorCodeEnum' field_errors: type: array items: $ref: '#/components/schemas/FieldError' DeviceSlotAssignment: type: object description: One device's target rack slot within a `reassign-slots` request. properties: device_id: type: string format: uuid rack_id: type: string format: uuid position: type: string format: decimal pattern: ^-?\d{0,3}(?:\.\d{0,1})?$ required: - device_id - position - rack_id ErrorCodeEnum: type: string description: >- Stable machine-readable error identifier. New members may be added within this API version; clients must tolerate unknown values. enum: - error - invalid - parse_error - authentication_failed - not_authenticated - permission_denied - not_found - method_not_allowed - not_acceptable - unsupported_media_type - conflict - enrollment_infrastructure_reference_pending - enrollment_infrastructure_reference_changed - unprocessable_entity - throttled - service_unavailable FieldError: type: object description: One input field's validation messages. required: - field - messages properties: field: type: string description: >- Dotted path to the offending input field, or to the collection row when the whole row is invalid (e.g. `filters.end_date`, `memberships.0.role`, `memberships.0`). messages: type: array minItems: 1 items: type: string securitySchemes: oauth2: type: oauth2 flows: {} cookieAuth: type: apiKey in: cookie name: sessionid ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.