Reads go back in time

  • Fix
  • Quorum 13

Difficulty 3 of 5

At 0:20 the primary crashes and a follower takes over. At 0:26 the old primary returns and replays 2,400 missed writes. Readers see a comment, reload, and it is gone. Keep stale reads under 30 and availability above 98 percent. Budget: 30 USD/month.

0:26. A comment vanished on reload. Graph: stale reads jump while the returned copy replays 2,400 writes.

Play level

SQLUsers800 req/sPostgres1 vCPU · 2 GB × 3
SQLUsers800 req/sPostgres1 vCPU · 2 GB × 3
The board at the start of the level
Read and write quorumsLeft and right arrows change R. Tap to change W.

W 3 + R 3 of 5 · every read sees the last write

Goals and limits

Stale reads
under 30
Availability
at least 98%
p99 latency
under 100 ms
Monthly cost
under 30 USD/mo
Edit limit
2
Traffic
800 req/s

Concepts

How players did

Player results load from the server.

All levels