Background

• Why do they need it?
  • Scalability
  • Simpler Code
  • Everyone’s doing it (hypecurve)
• Scalability
  • DB Master/Slave
  • Partitioning
  • Sharding
    • Like partitioning but with a natural key

Architecture

• Don’t get caught up in layers

• DDD
  • Value objects
  • Anti-corruption components
  • Sub-domains and bounded contexts
    • One to one relationship
      • Bounded context => sub-domain
• Beyond Layers
  • Service buses
• Concurrency begins to choke e.g. transactions on count then update
  • Connection pool dries up
  • Terrible wait for other users
• Regular CQRS may fall behind too
  • Eventually consistent - how long?

Approaches

• Event Driven Architecture
  • Event Sourcing
    • Non-blocking
    • Append only
• The business needs to be more flexible
  • Asking to scale will eventually require eventual consistency
  • Non-blocking and non-consistent frees contention
• Append only
  • Delta rows, +1, -1, +250 etc
  • No consistency, Sum(Delta)

  • Data volume becomes insane proportional to requests & commands, not inventory

  • Add snapshotting occasionally aggregating and truncating history
• CQRS as an approach, not cookie cutter