Problems / Databases, medium

Metrics: every scrape lands at once

A metrics system scrapes 400 targets a second on average, but scrapes line up every 15 seconds and 5× as many land at once on a 2-vCPU time-series database.

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Your goals

Success ≥ 99%, p99 ≤ 2 s.

Test cases

Like a coding problem, a solution has to pass every case, not just the one it was built for. Submit in the lab runs all 4; 1 of them are hidden until then.

  1. As given. The problem’s own traffic, scheduled failures and seed.
  2. Peak hour. 25% more traffic than the problem states, with the same failures.
  3. A server dies. One replica of the service with the most replicas is killed for part of the run.

The traffic

400 requests a second, with 5× bursts every 15 s for 30 seconds: 100% writes.

The system

What each component does in this design, and what calls it. The simulator mimics each one from these settings.

ComponentIts job hereSettings
Load balancerLoad balancerTraffic enters here.Calls Collector.Layer 4 balancers route by IP and port; layer 7 balancers read HTTP and can route by path or header.–
CollectorApp serviceLoad balancer forwards to it.Calls Time-series DB.Little's law: throughput ≈ concurrency ÷ latency. 200 slots at 50 ms serve about 4,000 req/s.3 replicas × 200 slots · timeout 4.0 s
Time-series DBTime-series databaseCollector calls it.Time-series databases compress by time and downsample old data to keep storage small.500 slots

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