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"content": "During a design discussion on audit trail strategy for financial transactions, the team decided to move from standard CRUD in PostgreSQL to an Event Sourcing architecture.\n\nproblem: Under the existing CRUD approach, updates overwrite previous states. When compliance audited transaction #8821, the team could not provide who changed the status from pending to approved because the prior state was lost.\n\nalternatives considered:\n1. Database triggers writing to a history_logs table (suggested by Charlie). Rejected because triggers only see raw row changes (e.g., status changed from 1 to 2) and lose business context -- they cannot capture why the change happened or the user intent behind it.\n\ndecision: Implement Event Sourcing. Store a sequence of immutable domain events (e.g., TransactionCreated, TransactionApproved, StatusUpdated) instead of mutable table states. Use Kafka as the immutable event log, and build materialized views in Postgres for fast reads on the frontend.\n\nimplementation plan:\n- Event producers: src/services/transactionService.ts\n- Consumer/store logic: src/events/eventStore.ts\n\nreference: Martin Fowler's Event Sourcing Pattern article -- identified as the industry-standard reference architecture for this pattern.",
"summary": "The team chose Event Sourcing with Kafka for immutable audit trails instead of CRUD or database triggers, to preserve full transaction history including business context and user intent for compliance requirements.",
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