Files
shopdb-flask/docs/adr/ADR-014-schema-lean-per-site.md
cproudlock 4995456136 docs: take one site's name, hosts and paths off the public wiki
The publishability gate caught internal tooling names and developer paths but
nothing site-specific, so roughly sixty leaks reached the wiki: the site name in
ten documents, real fleet hostnames in the collector and GE-Enforce examples, an
internal database name through the whole import guide, imaging-share paths, and
a maintainer's username as the Deciders line of every ADR and inside a generated
curl example.

None of it is a security matter on an air-gapped fleet. It matters because these
pages are read by engineers at other plants, and a document that names one site
throughout reads as that site's notes rather than a product's documentation -
which is exactly what it then gets treated as.

Examples now use neutral hostnames, the site is "the reference site" where the
distinction carries meaning, and ADRs are decided by "ShopDB maintainers". The
gate carries all of these patterns, so the next one fails a build.

Two documents leave docs/ because they were never written for an outside reader.
PROJECT-REVIEW.md is an internal health memo pinned to a commit from July, whose
headline finding (an untracked playbook) has since been fixed - it is history,
and git holds it. PILOT-DEPLOY.md is one site's own cutover runbook, complete
with a "re-measure before publishing" placeholder; it moves next to the loader
it belongs to, in scripts/site_imports/wjf/.

ADR-015 is AMENDED rather than rewritten. Its enforcement section still said
report-only and its backlog still listed hardcodes that are now cleared, which
left the record contradicting itself. The amendment says what changed and why
the report-only period ended; the original text stays, because what the decision
looked like when it was taken is the part worth keeping.

Also corrects llms.txt's response envelope, which had errors at the top level
and pagination at meta.total. Both are nested one deeper, so anything written
against that description read undefined on every error it tried to handle.
2026-08-14 15:38:27 -04:00

7.3 KiB

ADR-014: Schema-lean per-site builds (retire cross-plugin FKs, lift plugin tables)

  • Status: ACCEPTED
  • Date: 2026-07-19
  • Deciders: ShopDB maintainers
  • Relates to: ADR-008 (per-plugin migration ownership), ADR-013 (plugin catalog + lean per-site builds), ADR-001 (asset model)

Context

ADR-013 delivered lean per-site builds for plugin CODE (backend tree + frontend bundle carry only chosen plugins). One residual was left, explicitly deferred: the DATABASE. The core Alembic baseline (68b3947ae14f) creates EVERY table, including ~30 plugin-owned tables (PLUGIN_TABLE_OWNERS). Each plugin's own baseline is a stamp-only no-op (the core chain already made its tables, per ADR-008). So a lean site that omits a plugin still creates that plugin's tables, empty and unused.

The deferral cited a blocker: "the computers-owned installedapps table FKs machines.machineid while computers declares no dependency on machines; reversing the cutover would introduce undeclared hard deps or drop FKs; neither is decided." Investigation refined this:

The cross-boundary foreign keys into the machines plugin table are ALL held by DEAD legacy tables/columns that predate the asset model (ADR-001) and the per-plugin cutover (ADR-008), and are queried nowhere in the codebase:

  • machinerelationships (child/parentmachineid -> machines) - superseded by assetrelationships. No model, no query.
  • printerdata (machineid -> machines) - the pre-cutover printers table, superseded by the printers plugin. No model, no query.
  • installedapps (machineid -> machines) - a standalone machine-app link table; the live relationship is computerinstalledapps (FK to computers only). The standalone table has no model, no query.
  • communications.machineid (-> machines) - a legacy column on the core communications table (which is now assetid-based). Not read anywhere.

No LIVE plugin table hard-FKs another plugin's table. computerinstalledapps FKs only computers.computerid (intra-plugin). So the blocker is dead cruft, not live design.

Decision

Two phases, both leaving existing databases correct.

Phase 1: retire the dead cross-boundary cruft - ALREADY DONE

Investigation found this is already accomplished by existing migrations: 7a01_adr001_position_contract and 7c01_drop_legacy_machine drop machinerelationships, printerdata, installedapps, and communications.machineid (with its FK). The current schema (verified on the dev database) has none of them. So the cross-plugin FK blocker ADR-013 cited no longer exists in the live schema - only in the baseline's transient create-then-later-drop. No new migration is needed for Phase 1.

Precedent: ADR-001 dropped a cross-plugin FK the same way (usbcheckouts.machineid -> machines became a soft sentinel).

Enabling change (executed now): idempotent create_plugin_tables

shopdb/plugins/alembic_template.py:create_plugin_tables now skips any table that already exists (inspects the bind first) instead of raising. This is the mechanism Phase 2 needs: a plugin anchor can create its tables on a fresh lean install AND be a safe no-op on an existing database that already has them from the pre-cutover core baseline. Correct and inert regardless of Phase 2 (no current caller creates against a populated schema). Verified against the plugin-migration suite.

Phase 2 (executed): prune not-installed plugin tables after upgrade

Two mechanisms were weighed to make a lean site's database carry only core + chosen-plugin tables:

  • Relocate (rejected): pull every plugin-table create/alter out of the core chain into the plugin baselines, so the core chain never creates a not-installed plugin's table. Measurement killed this: plugin tables are created and altered across ~15 released core migrations (baseline plus 7c04, 7d05, 7d08, 7d13, 7d15, 7d16, 7d17, ...), not just the baseline. Because the whole core chain runs before any plugin chain, removing a table's create from core while a later core migration still alters it breaks FULL installs too, so relocation means surgically rewriting ~15 released migrations - the highest blast radius in the project - for a purely cosmetic gain (the omitted tables are empty and the lean CODE build already never loads the plugin).

  • Prune-after-upgrade (chosen): leave the entire core chain untouched. Add flask plugin prune-schema, which drops the tables of every plugin in PLUGIN_TABLE_OWNERS that is not installed on this site. Run once at deploy, after flask db upgrade and flask plugin upgrade-all. Same end state (core + chosen tables) with near-zero blast radius: no released migration is edited, and an existing full site is unaffected because it never runs the command.

prune-schema drops by table name (no plugin-code import), so it works on a lean image where the omitted plugin's directory is absent. It is a dry-run by default and refuses to drop a table that holds rows unless --force, so a misfire on a populated site cannot silently delete data. Because the core chain seeds a few plugin reference tables (e.g. 7d05 inserts default access protocols), initial lean provisioning uses --force - at that point the tables hold only migration-seeded defaults, before any site data exists.

The idempotent create_plugin_tables (enabling change above) is what lets a lean site later ADD an omitted plugin: its anchor recreates the pruned tables.

Verified end to end on MySQL: fresh full install (86 tables) then prune is a no-op; fresh lean install (machines + printers) then prune drops the other 19 plugin tables, leaving core + chosen; second prune is a no-op; the non-empty guard refuses without --force. Four SQLite regression tests pin the behavior (tests/test_plugin_prune_schema.py), running in the backend CI job via the real CLI runner: drop-only-not-installed, full-site no-op, refuse-non-empty, and force-drops-non-empty.

Consequences

Positive

  • A lean site's database contains only core + chosen-plugin tables, with no edit to any released migration (near-zero blast radius).
  • The cross-plugin FK blocker ADR-013 cited is gone (dead cruft, dropped by existing migrations), so plugin schemas are already FK-independent.
  • Adding an omitted plugin to a lean site later just works: the idempotent anchor recreates its tables.

Negative / risk

  • prune-schema is destructive by nature; the row-count guard + dry-run default + required --force for non-empty tables contain that. It is a deploy-time provisioning step, not something to run casually on a live populated site.
  • A lean fresh install still transiently creates then drops the omitted plugins' tables (the core chain builds them, prune removes them). Harmless and one-time at provisioning; the trade for not touching the released baseline.

Implementation

  • Phase 1: nothing to do - the dead cross-boundary FK objects were already dropped by existing migrations 7a01_adr001_position_contract and 7c01_drop_legacy_machine; verified absent on a fresh full MySQL upgrade.
  • Enabling change: create_plugin_tables made idempotent (shopdb/plugins/alembic_template.py).
  • Phase 2: flask plugin prune-schema (shopdb/plugins/cli.py), dry-run by default, --yes to execute, --force for non-empty tables. Deploy order: flask db upgrade -> flask plugin upgrade-all -> flask plugin prune-schema --yes --force. Regression tests in tests/test_plugin_prune_schema.py (run in the backend CI job).