Replace deep offset paging with a stable inbox cursor
An operator reaches old open work through hundreds of pages. Each offset request scans and discards an increasing number of matching rows.
- Focused work estimate
- 4h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Pagination · Query performance
Estimated field mix
- Database engineering40%
- API design40%
- Performance engineering20%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional maintenance service lists open work orders beside years of closed history. A query that was cheap in a small demo now scans far more rows than it returns. Recreate the schema and synthetic workload locally; no customer database or supplied fixture is assumed.
Setup prerequisites
- Create an isolated local database with tenants, work orders and assignment history.
- Seed 200,000 synthetic work orders with documented skew and a repeatable random seed; record PostgreSQL version, settings and resource limits.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Use a stable sort tuple with a unique tie-breaker and an opaque versioned cursor.
- Bind the cursor to the tenant and filter contract; reject mismatched or malformed cursors.
- Document concurrent-insert behavior and preserve a bounded page size without promising a snapshot across requests.
Implementation constraints
- Measure shallow and deep page requests against the same fixture; keep the response contract explicit for clients migrating from offsets.
Verification to include
- Traverse the unchanged fixture and compare all returned IDs with the expected sorted set without duplicates or omissions.
- Insert a tied-timestamp row between requests and test the documented behavior; reject a cursor from another tenant.
Deliverables
- Cursor contract, implementation and depth-comparison report
Rollout and recovery
Offer the cursor route as an explicit version and migrate the local client behind a switch; retain the offset route during rehearsal.
Value of the work
For the engineer: Practice reading execution plans, balancing read and write cost, and validating performance without weakening tenant boundaries.
For the team: Create reproducible query diagnostics and reversible index or query proposals for an operational application.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.