NexHealth Software Engineer
Interview Guide

1–2 sentences introducing the category and what it tests.

1–2 sentences introducing the category and what it tests.

The egress service delivers about 1,500 webhooks per second across roughly 40,000 destinations, each call bounded by a 10 second timeout. Maintain, per destination, the failure rate over the trailing 60 seconds so a caller can ask before dispatch whether the circuit should open. Attempts arrive as (destination_id, finished_at_ms, outcome). Requirement: amortised O(1) per attempt, with total memory bounded by the destination count rather than by traffic. Give the structure, its exact memory, and the rule that stops a destination with three attempts from opening a circuit.

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

A tenant on the standard plan may hold at most 50 resources with status='active'. The create handler runs SELECT count(*) FROM resource WHERE tenant_id = $1 AND status = 'active', compares to 50, then inserts. Two creates arrive 3 ms apart on different instances and the tenant lands at 51. Name the anomaly, say whether PostgreSQL 16 READ COMMITTED or REPEATABLE READ prevents it and why, then give an implementation that holds the cap at READ COMMITTED with the exact statements. Finally, say what changes when the cap is 'at most one running export per tenant' on job_run.

Bullet list of realistic example questions: How would you design a robust synchronization mechanism for handling intermittent connections with legacy medical record systems? Walk through how you would diagnose and resolve a latency bottleneck in an external API integration layer. What strategies do you use to ensure zero-downtime database schema migrations in a high-traffic production environment? How would you approach building a fault-tolerant webhook delivery system for third-party developers?

Bullet list of realistic example questions: Write a function to parse, validate, and transform incoming healthcare data payloads into a standardized internal schema. Implement a rate limiter to protect critical API endpoints from sudden traffic spikes or denial-of-service patterns. Given a stream of patient appointment events, write code to aggregate and query time-slot availability efficiently. Debug an asynchronous data processing pipeline where jobs are occasionally dropping or timing out under load.

1–2 sentences introducing the category and what it tests.

Bullet list of realistic example questions: Design a secure data-storage architecture that complies with strict healthcare privacy standards while allowing fast querying. How would you architect a scalable notification engine that supports SMS, email, and push notifications across multiple tenants? Explain how you would structure a microservices-based API platform to handle high concurrency and sudden usage surges. Discuss the trade-offs between using event-driven architecture versus synchronous REST calls for cross-service communication.

The cached listing read path serves about 14k reads/second at an 85% hit rate. p99 sits at 35 ms for 57 seconds, jumps to 900 ms for 3, and repeats. During each spike the primary shows several hundred identical listing queries starting within the same millisecond, all carrying one large tenant's id. Cache entries use a 60-second TTL. Give the mechanism, the ordered checks, the fix, and the correctness hazard your fix must not introduce.