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The patterns

How to apply the patterns

Core patterns

Decomposition

Deployment patterns

Cross cutting concerns

Communication style

External API

Service discovery

Reliability

Data management

Security

Testing

Observability

UI patterns


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Pattern: Transaction log tailing

Context

You have applied the Event-driven architecture pattern. In order to be reliable, services must atomically publish events whenever their state changes. It is not viable to use a distributed transaction that spans the database and the message broker.

Problem

How to reliably/atomically publish events whenever state changes?

Forces

  • 2PC is not an option

Solution

Tail the database transaction log and publish each change as an event.

Example

Resulting context

This pattern has the following benefits:

  • No 2PC
  • No application changes required
  • Guaranteed to be accurate

This pattern has the following drawbacks:

  • Relatively obscure
  • Database specific solutions
  • Tricky to avoid duplicate publishing
  • Low level DB changes make difficult to determine the business level events

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