feat: migrate to Postgres + pgvector with Alembic scaffolding

Switch the default database from SQLite to Postgres + pgvector (via
pgvector/pgvector:pg16 Docker image) to support the upcoming vision
pipeline (embeddings, OCR, object detection, face clustering).

- Add `db` service to docker-compose.yml with healthcheck
- Wire `alembic upgrade head` into backend CMD before uvicorn
- Bootstrap empty 0001_baseline revision (schema still owned by create_all)
- Guard SQLite-only PRAGMAs and inline ALTERs behind _is_sqlite flag
- Run `CREATE EXTENSION IF NOT EXISTS vector` on Postgres init
- Add asyncpg, psycopg2-binary, pgvector to requirements
- Provide docker-compose.sqlite.yml escape hatch for legacy SQLite mode

Fresh DB + rescan assumed — no SQLite→Postgres data migration.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/alembic.ini

@@ -0,0 +1,48 @@
+# Alembic configuration for PhotoVault.
+#
+# The actual database URL is loaded at runtime by alembic/env.py from the
+# DATABASE_URL environment variable (with the async driver suffix stripped).
+# The placeholder below is only used for `alembic revision --autogenerate`
+# when no env var is set.
+
+[alembic]
+script_location = alembic
+prepend_sys_path = .
+version_path_separator = os
+sqlalchemy.url = postgresql+psycopg2://mulita:mulita@localhost:5432/mulita
+
+[post_write_hooks]
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

backend/alembic/env.py

@@ -0,0 +1,96 @@
+"""
+Alembic environment for PhotoVault.
+
+Pulls DATABASE_URL from the environment so the same migrations work in
+docker compose and locally. Strips the async driver suffix because Alembic
+runs synchronously via psycopg2.
+
+Future-migration note
+---------------------
+Fresh installs run `Base.metadata.create_all` in `app.database.init_db`
+*before* migrations would normally apply, so any migration that adds a
+column / index / table to an object the model already declares will see
+that object already present. Write migrations defensively:
+
+    op.execute("ALTER TABLE photos ADD COLUMN IF NOT EXISTS new_col TEXT")
+    op.execute("CREATE INDEX IF NOT EXISTS ix_foo ON foo(bar)")
+
+For brand-new tables that the model also declares, the same applies — use
+`op.execute("CREATE TABLE IF NOT EXISTS ...")` or check first.
+"""
+from logging.config import fileConfig
+import os
+import sys
+from pathlib import Path
+
+from sqlalchemy import engine_from_config, pool
+from alembic import context
+
+# Make `app` importable from this script.
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
+from app.database import Base  # noqa: E402
+# Import all models so they're registered on Base.metadata for autogenerate.
+from app.models import (  # noqa: E402, F401
+    Photo,
+    Folder,
+    SourceRoot,
+    Tag,
+    Heap,
+    HeapPhoto,
+    Embedding,
+)
+
+config = context.config
+
+# Resolve DATABASE_URL from env. Strip async driver suffixes — Alembic
+# uses sync drivers.
+db_url = os.environ.get("DATABASE_URL") or config.get_main_option("sqlalchemy.url")
+if db_url:
+    if "+asyncpg" in db_url:
+        db_url = db_url.replace("+asyncpg", "+psycopg2")
+    elif db_url.startswith("postgresql://"):
+        db_url = db_url.replace("postgresql://", "postgresql+psycopg2://", 1)
+    elif "+aiosqlite" in db_url:
+        db_url = db_url.replace("+aiosqlite", "")
+    config.set_main_option("sqlalchemy.url", db_url)
+
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode (emit SQL only)."""
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations against a live database."""
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection,
+            target_metadata=target_metadata,
+        )
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

backend/alembic/script.py.mako

@@ -0,0 +1,26 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}

backend/alembic/versions/0001_baseline.py

@@ -0,0 +1,27 @@
+"""baseline (empty)
+
+Revision ID: 0001_baseline
+Revises:
+Create Date: 2026-04-10
+
+The current schema is created by SQLAlchemy `Base.metadata.create_all` in
+`app.database.init_db()` on first boot. Alembic only owns deltas from
+PR3 onward. This baseline is intentionally empty so `alembic upgrade head`
+on a fresh DB simply creates the `alembic_version` table and stamps it.
+"""
+from typing import Sequence, Union
+
+
+# revision identifiers, used by Alembic.
+revision: str = "0001_baseline"
+down_revision: Union[str, None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    pass
+
+
+def downgrade() -> None:
+    pass

backend/app/config.py

@@ -39,9 +39,11 @@ class MulitaConfig(BaseModel):
 
 class Settings(BaseSettings):
     """Application settings"""
-    # Database
+    # Database — Postgres + pgvector by default. The SQLite escape hatch
+    # remains supported via the docker-compose.sqlite.yml override and by
+    # setting DATABASE_URL=sqlite+aiosqlite:///... in .env for local dev.
     database_url: str = Field(
-        default="sqlite+aiosqlite:///data/db/mulita.db",
+        default="postgresql+asyncpg://mulita:mulita@db:5432/mulita",
         env="DATABASE_URL"
     )
     

backend/app/database.py

@@ -1,38 +1,50 @@
 """
-Database configuration and session management
+Database configuration and session management.
+
+Schema management strategy
+--------------------------
+Postgres (default): Alembic owns schema deltas. `alembic upgrade head` is
+run before the app starts (in the container CMD). `init_db()` calls
+`create_all` afterward as the source of truth for fresh installs — it is
+idempotent for existing tables and creates any tables defined on
+`Base.metadata` that don't yet exist. Future Alembic migrations should be
+written defensively (`IF NOT EXISTS` etc.) so they remain safe to run on a
+fresh DB where `create_all` has already laid down the same objects.
+
+SQLite (escape hatch via docker-compose.sqlite.yml): no Alembic. The
+historical inline ALTER TABLE block stays in place so existing dev
+installs keep upgrading.
 """
 from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine, async_sessionmaker
 from sqlalchemy.orm import declarative_base
-from sqlalchemy import event, text
+from sqlalchemy import text
 import logging
-import os
 from pathlib import Path
 
 from app.config import settings
 
 logger = logging.getLogger(__name__)
 
-# Create database directory if it doesn't exist
-db_path = Path(settings.database_url.replace("sqlite+aiosqlite:///", ""))
-db_path.parent.mkdir(parents=True, exist_ok=True)
+_is_sqlite = settings.database_url.startswith("sqlite")
+_is_postgres = settings.database_url.startswith("postgresql")
 
-# Create async engine
-# SQLite doesn't support pool configuration
-if "sqlite" in settings.database_url:
+if _is_sqlite:
+    db_path = Path(settings.database_url.replace("sqlite+aiosqlite:///", ""))
+    db_path.parent.mkdir(parents=True, exist_ok=True)
     engine = create_async_engine(
         settings.database_url,
-        echo=False,  # Set to True for SQL debugging
+        echo=False,
         connect_args={
-            "check_same_thread": False,  # SQLite specific
-            "timeout": 30
-        }
+            "check_same_thread": False,
+            "timeout": 30,
+        },
     )
 else:
     engine = create_async_engine(
         settings.database_url,
-        echo=False,  # Set to True for SQL debugging
+        echo=False,
         pool_size=settings.performance.db_pool_size,
-        pool_recycle=settings.performance.db_pool_recycle
+        pool_recycle=settings.performance.db_pool_recycle,
     )
 
 # Create async session factory
@@ -59,26 +71,32 @@ async def init_db():
         # Import all models to register them with Base
         from app.models import Photo, Folder, SourceRoot, Tag, PhotoTag, Heap, HeapPhoto, Embedding
 
+        # Postgres: ensure pgvector is available before create_all touches
+        # any Vector columns (added in later PRs but the extension is cheap
+        # and idempotent to create now).
+        if _is_postgres:
+            await conn.execute(text("CREATE EXTENSION IF NOT EXISTS vector"))
+
         # Create all tables. Note: create_all only creates *missing* tables —
         # it does NOT add new columns to existing tables when the model gains
-        # them. Anything new on an existing table needs an explicit ALTER
-        # below.
+        # them. On Postgres, Alembic handles deltas; on SQLite, the inline
+        # ALTER block below is the legacy fallback.
         await conn.run_sync(Base.metadata.create_all)
 
-        # Enable WAL mode for SQLite (better concurrency)
-        if "sqlite" in settings.database_url:
+        gps_columns_added = False
+
+        if _is_sqlite:
+            # WAL mode for better concurrency.
             await conn.execute(text("PRAGMA journal_mode=WAL"))
             await conn.execute(text("PRAGMA synchronous=NORMAL"))
             await conn.execute(text("PRAGMA cache_size=10000"))
             await conn.execute(text("PRAGMA temp_store=MEMORY"))
 
-        # ── Idempotent column adds ────────────────────────────────────────
-        # The project does not use Alembic; we lean on create_all + a small
-        # set of inline ALTER TABLE statements for the columns we've added
-        # post-launch. SQLite supports ADD COLUMN but not "IF NOT EXISTS"
-        # for columns, so introspect via PRAGMA first. Each entry is
-        # (column_name, ALTER statement). Add new columns at the bottom.
-        if "sqlite" in settings.database_url:
+            # ── Idempotent column adds (SQLite only) ─────────────────────
+            # SQLite supports ADD COLUMN but not "IF NOT EXISTS" for
+            # columns, so introspect via PRAGMA first. Each entry is
+            # (column_name, ALTER statement). Add new columns at the
+            # bottom. On Postgres these live in Alembic migrations.
             existing_cols = {
                 row[1]
                 for row in (
@@ -94,18 +112,12 @@ async def init_db():
                 ("latitude", "ALTER TABLE photos ADD COLUMN latitude REAL"),
                 ("longitude", "ALTER TABLE photos ADD COLUMN longitude REAL"),
             ]
-            # Track whether the GPS columns were just added so we can kick
-            # off a one-shot backfill of existing photos at the end of init.
-            gps_columns_added = False
             for col_name, alter_sql in pending_alters:
                 if col_name not in existing_cols:
                     logger.info(f"Adding photos.{col_name} column")
                     await conn.execute(text(alter_sql))
                     if col_name in ("latitude", "longitude"):
                         gps_columns_added = True
-            # Indexes for the new duplicate-detection columns. CREATE INDEX
-            # IF NOT EXISTS is supported on SQLite so this is safe to run
-            # every startup.
             await conn.execute(
                 text("CREATE INDEX IF NOT EXISTS ix_photos_phash ON photos(phash)")
             )
@@ -124,11 +136,12 @@ async def init_db():
 
         logger.info("Database initialized successfully")
 
-        # If we just introduced the GPS columns on an existing install, kick
-        # off a one-shot backfill so the Map view is populated without a
-        # manual full re-scan. Imported lazily to avoid pulling Celery into
-        # the import graph for non-worker processes that don't need it.
-        if "sqlite" in settings.database_url and gps_columns_added:
+        # If we just introduced the GPS columns on an existing SQLite
+        # install, kick off a one-shot backfill so the Map view is
+        # populated without a manual full re-scan. Postgres installs are
+        # always fresh (no SQLite→PG migration path), so this code path
+        # is SQLite-only.
+        if _is_sqlite and gps_columns_added:
             try:
                 from app.tasks.scan import backfill_gps
                 backfill_gps.delay()
@@ -137,8 +150,9 @@ async def init_db():
                 logger.warning(f"Could not queue backfill_gps task: {e}")
 
 async def create_fts_table():
-    """Create Full-Text Search table for SQLite"""
-    if "sqlite" in settings.database_url:
+    """Create Full-Text Search table for SQLite. On Postgres this is
+    replaced by a tsvector column on the photos table (added in PR5)."""
+    if _is_sqlite:
         async with engine.begin() as conn:
             # Create FTS5 virtual table for full-text search
             await conn.execute(text("""

backend/requirements.txt

@@ -5,7 +5,10 @@ python-multipart==0.0.6
 
 # Database
 sqlalchemy[asyncio]==2.0.25
-aiosqlite==0.19.0
+aiosqlite==0.19.0           # SQLite escape hatch (docker-compose.sqlite.yml override)
+asyncpg==0.29.0             # async Postgres driver (default)
+psycopg2-binary==2.9.9      # sync Postgres driver, used by Alembic CLI
+pgvector==0.2.5             # pgvector SQLAlchemy types
 alembic==1.13.1
 
 # Redis and Celery

docker-compose.sqlite.yml

@@ -0,0 +1,47 @@
+# SQLite escape hatch override.
+#
+# Usage (omit the `db` service from the up command):
+#
+#   docker compose -f docker-compose.yml -f docker-compose.sqlite.yml \
+#       up frontend backend worker redis
+#
+# This pins the backend and worker to the legacy SQLite database file at
+# /data/db/mulita.db (in the existing db_data volume), drops the dependency
+# on Postgres, and skips Alembic — the SQLite schema is still managed by
+# the inline ALTERs in app/database.py:init_db.
+#
+# Vision features that depend on pgvector (PR4 onward) will refuse to enable
+# in this mode; the search/embedding endpoints will return 503 with a clear
+# error pointing back at the default Postgres setup.
+
+services:
+  backend:
+    command: sh -c "uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload"
+    environment:
+      - DATABASE_URL=sqlite+aiosqlite:////data/db/mulita.db
+      - REDIS_URL=redis://redis:6379
+      - CELERY_BROKER_URL=redis://redis:6379
+      - CELERY_RESULT_BACKEND=redis://redis:6379
+      - PHOTO_DIRS=${PHOTO_DIRS:-/photos}
+      - ALLOWED_ORIGINS=${ALLOWED_ORIGINS:-*}
+      - LOG_LEVEL=${LOG_LEVEL:-INFO}
+      - TZ=${TZ:-UTC}
+    depends_on:
+      redis:
+        condition: service_started
+
+  worker:
+    environment:
+      - DATABASE_URL=sqlite+aiosqlite:////data/db/mulita.db
+      - REDIS_URL=redis://redis:6379
+      - CELERY_BROKER_URL=redis://redis:6379
+      - CELERY_RESULT_BACKEND=redis://redis:6379
+      - PHOTO_DIRS=${PHOTO_DIRS:-/photos}
+      - CELERYD_CONCURRENCY=${CELERYD_CONCURRENCY:-4}
+      - LOG_LEVEL=${LOG_LEVEL:-INFO}
+      - TZ=${TZ:-UTC}
+    depends_on:
+      redis:
+        condition: service_started
+      backend:
+        condition: service_started

docker-compose.yml

@@ -1,5 +1,3 @@
-version: '3.8'
-
 services:
   frontend:
     build:
@@ -36,9 +34,13 @@ services:
       - ${PHOTO_DIRS:-./photos}:/photos:rw
       - thumbs_data:/data/thumbs
       - proxies_data:/data/proxies
-      - db_data:/data/db
+      - db_data:/data/db   # retained so the docker-compose.sqlite.yml override has somewhere to put mulita.db
+    # Run Alembic migrations before starting uvicorn. On a fresh Postgres
+    # the empty 0001 baseline is a no-op stamp; create_all in init_db then
+    # builds the schema.
+    command: sh -c "alembic upgrade head && uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload"
     environment:
-      - DATABASE_URL=sqlite+aiosqlite:////data/db/mulita.db
+      - DATABASE_URL=postgresql+asyncpg://mulita:mulita@db:5432/mulita
       - REDIS_URL=redis://redis:6379
       - CELERY_BROKER_URL=redis://redis:6379
       - CELERY_RESULT_BACKEND=redis://redis:6379
@@ -47,7 +49,10 @@ services:
       - LOG_LEVEL=${LOG_LEVEL:-INFO}
       - TZ=${TZ:-UTC}
     depends_on:
-      - redis
+      redis:
+        condition: service_started
+      db:
+        condition: service_healthy
     networks:
       - mulita-network
     restart: unless-stopped
@@ -65,7 +70,7 @@ services:
       - proxies_data:/data/proxies
       - db_data:/data/db
     environment:
-      - DATABASE_URL=sqlite+aiosqlite:////data/db/mulita.db
+      - DATABASE_URL=postgresql+asyncpg://mulita:mulita@db:5432/mulita
       - REDIS_URL=redis://redis:6379
       - CELERY_BROKER_URL=redis://redis:6379
       - CELERY_RESULT_BACKEND=redis://redis:6379
@@ -74,12 +79,34 @@ services:
       - LOG_LEVEL=${LOG_LEVEL:-INFO}
       - TZ=${TZ:-UTC}
     depends_on:
-      - redis
-      - backend
+      redis:
+        condition: service_started
+      backend:
+        condition: service_started
+      db:
+        condition: service_healthy
     networks:
       - mulita-network
     restart: unless-stopped
 
+  db:
+    image: pgvector/pgvector:pg16
+    container_name: mulita-db
+    environment:
+      POSTGRES_USER: mulita
+      POSTGRES_PASSWORD: mulita
+      POSTGRES_DB: mulita
+    volumes:
+      - pg_data:/var/lib/postgresql/data
+    networks:
+      - mulita-network
+    restart: unless-stopped
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U mulita -d mulita"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+
   redis:
     image: redis:7-alpine
     container_name: mulita-redis
@@ -103,3 +130,4 @@ volumes:
   proxies_data:
   db_data:
   redis_data:
+  pg_data: