# Research: PostgreSQL Database Replacement

> For the complete documentation index, see [llms.txt](https://traderx.finos.org/llms.txt).

[Learning Guide — PostgreSQL Database Replacement](https://traderx.finos.org/docs/learning/state-005-postgres-database-replacement.md): purpose, walkthrough, and related learning states.

# Research: PostgreSQL Database Replacement

## Objective

Define the transition from state `004` to `005` by replacing H2 with PostgreSQL while preserving behavior.

## Inputs Reviewed

*   `spec.md`
*   `plan.md`
*   `tasks.md`
*   `requirements/functional-delta.md`
*   `requirements/nonfunctional-delta.md`
*   `system/architecture.md`
*   `system/runtime-topology.md`

## Key Decisions

1.  Use PostgreSQL as the default SQL persistence engine for this branch.
2.  Preserve application-level behaviors and API compatibility from predecessor state.
3.  Keep migration reversible and clearly isolated as a state-specific delta.