Spike: prove that a Django-managed archive database works

[bjester]

Overview

This spike (milestone M0) tests the risky parts of the archive design before other work starts. The spike code is temporary. The result is a set of findings, and changes to the design spec if a finding disagrees with it.

Background & Motivation

The disk export writes an archive: a SQLite file that Django manages as a second database. Morango has never used a second database at runtime. Several parts of the design depend on Django and django-mptt behavior that nobody tested in this codebase.

If one of these assumptions is wrong, later tasks build on a bad base. A short spike finds these problems early and at low cost.

Design: spec. Plan: implementation plan, Task 1.

Description & Expected Outcomes

The spike answers these questions:

• Can Django 3.2 add a database alias at runtime, with full default settings?
• Can MigrationExecutor create all morango tables in that alias, without the contenttypes app?
• Does django-mptt send queries to the default database when a certificate is saved with save(using=alias)?
• Can bulk_create with explicit tree fields write a certificate chain that parent walks can read?
• Does PRAGMA auto_vacuum=INCREMENTAL, set before migration, let PRAGMA incremental_vacuum shrink the file?
• Can the alias be removed again, so that no trace stays in connections.databases?

The spike runs on a SQLite host and on a PostgreSQL host.

Deliverables & Contracts

The spike delivers:

• Written findings for each question.
• Updates to spec §3.3 or §3.5 when a finding disagrees with the spec.
• No code that stays in the repository.

Acceptance Criteria

• Each question has a recorded answer, with the host database (SQLite or PostgreSQL) for each result.
• If a finding disagrees with the spec, the spec is updated before Explicit database handle for sync database access #365 starts.
• The tests/testapp/tests/spike/ directory does not exist at the end of the task.

Technical Pointers & Architecture

• Target Components: Django connections handling, django.db.migrations.executor.MigrationExecutor, morango/models/certificates.py (Certificate, an MPTT model).
• Related Patterns: morango/deferrable_foreign_keys.py already works with schema_editor.connection in a migration.
• Data Model & Schema Considerations: The morango migrations declare no dependencies on other apps (0001_squashed_0024…).
• Resilience & Failure Modes: The spike records whether a restrictive router or a missing default setting causes a clear error.

Notes & Tradeoffs

• Dependencies: Blocked by: none. Blocks: Explicit database handle for sync database access #365, Create and discard an archive database file #378.
• Testing Requirements: Run on the default tox environment and on tox -e postgres.
• Tradeoffs & Alternatives Considered: The spec rejects a custom sqlite3 schema. If this spike fails, that decision needs review.

Metadata

• Complexity: Medium
• Target Branch: release-v0.9.x

AI Usage

Drafted with Claude (Claude Code) from the approved design spec and implementation plan. The author reviewed the requirements, and the code references were checked against the release-v0.9.x codebase.