Project Storage Architecture

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Oak persists projects in a database (SQLite by default, PostgreSQL supported), with write-through persistence: every edit is committed to the database as it happens — there is no Save button and nothing to lose. The .ove XML file, OTIO and FCPXML are import/export formats, not the working store.

Design principles

Aggregate-granular persistence, not full relational mapping. The database stores four things: project metadata, key/value settings, periodic full snapshots, and a per-node command journal. Domain semantics (timeline structure, node connections, keyframes, effect chains) stay inside each node's XML payload. A project is exactly "the node graph plus settings" — nothing else — so node granularity is a closed, complete model.
One serialization truth. The node XML in the database is the same document the .ove serializer produces (oaknode::serializer). New features (e.g. adjustment layers) extend the XML schema only — the database schema never changes.
The journal is produced by diffing, not by instrumenting commands. After every undoable command the in-memory project is re-serialized and compared node-by-node with the previous state; changed/added/ removed nodes each become one journal row. Existing and future command types are covered automatically.
The journal is the persistent undo history. Replaying applies each node's newest image in command order; rewinding applies the previous images in reverse. Undo survives restarts.

Schema (SQLite / PostgreSQL, sea-orm)

projects(id PK, uuid UNIQUE, name, schema_ver, created_at, modified_at, command_seq)
settings(project_id FK, key, value, PK(project_id, key))
snapshots(project_id FK, command_seq, payload, written_at, PK(project_id, command_seq))
journal(project_id FK, seq, node_identity, kind, old_xml, new_xml, at,
        PK(project_id, seq, node_identity))

snapshots.payload is the full project XML, written every Storage/SnapshotIntervalSec (default 600) while dirty, pruned to the newest 3. It only accelerates loading — the journal alone can rebuild the project from scratch.
journal rows are whole-node before/after images: old_xml is NULL for created nodes, new_xml is NULL for removed nodes. Loading takes the newest snapshot and replaces each node with its newest image in seq order; rewinding to command N applies old_xml backwards. node_identity = 0 is the settings pseudo-node.
Every command is one synchronous transaction (journal rows + command_seq + 1), so a kill -9 loses zero commands.
Storage/JournalRetentionDays (default 0 = keep forever) bounds the undo window; rows are kilobytes each.

Timeline representation

The timeline is a chain of node references inside node XML:

sequence ──<tracklists>──▶ tracklist ──<tracks>──▶ track ──<blocks>──▶ clip ──<footage>──▶ footage

The clip row carries its timeline range (<range in out/>), media offset (<media_in>) and footage reference; effect chains are connection records inside the effect nodes' XML. Loading re-links these identities in two passes (see oaknode::serializer), so no join tables are needed. Timeline edits map to a handful of node rows: moving a clip touches its track and the clip; splitting adds one node and updates two; ripple edits touch the affected tracks and delete the removed clips.

Write-through flow

A facade undo push (oakengine_undo_push, group end, undo/redo/ jump) succeeds.
The project is re-serialized in memory (microseconds to low milliseconds) and diffed against the last state.
One transaction writes the changed node rows, bumps command_seq and modified_at.
A background thread writes snapshots latest-wins; on exit the queue is flushed.

Import / export

Import: .ove / .otio / .fcpxml are parsed by their existing oakstorage backends and inserted as a new project row with kind = 'import' journal entries.
Export: the in-memory serialization is written through the ove-xml or otio backend; nothing is read from or written to the database beyond the current state.

Multi-writer and platforms

v1 assumes a single writer per database (SQLite busy_timeout, PG row locks). Multi-writer collaboration is future work (M14). The default database is a single user-level SQLite file; PostgreSQL is selected with an oakdb+pg:// URI.

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