perf(backend): index roms (platform_id, fs_size_bytes)

backend/alembic/versions/0097_roms_platform_fs_size_index.py

@@ -0,0 +1,40 @@
+"""Add composite index on roms (platform_id, fs_size_bytes)
+
+GET /api/platforms and GET /api/stats both sum roms.fs_size_bytes (per platform
+and across the whole library). fs_size_bytes was not part of any index, so the
+database had to read actual rows from the very wide, JSON-heavy roms table,
+taking 5-11s on large libraries. This composite index lets both sums resolve as
+index-only scans that never touch the wide rows; the optimizer picks it for both
+query shapes on its own.
+
+Revision ID: 0097_roms_platform_fs_size_index
+Revises: 0096_fix_virtual_collections
+Create Date: 2026-07-16 00:00:00.000000
+
+"""
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "0097_roms_platform_fs_size_index"
+down_revision = "0096_fix_virtual_collections"
+branch_labels = None
+depends_on = None
+
+INDEX_NAME = "idx_roms_platform_fs_size"
+INDEX_COLUMNS = ["platform_id", "fs_size_bytes"]
+
+
+def upgrade() -> None:
+    with op.batch_alter_table("roms", schema=None) as batch_op:
+        batch_op.create_index(
+            INDEX_NAME,
+            INDEX_COLUMNS,
+            unique=False,
+            if_not_exists=True,
+        )
+
+
+def downgrade() -> None:
+    with op.batch_alter_table("roms", schema=None) as batch_op:
+        batch_op.drop_index(INDEX_NAME, if_exists=True)

backend/models/rom.py

@@ -268,6 +268,9 @@ class Rom(BaseModel):
             "tgdb_id",
             "id",
         ),
+        # Covering index so per-platform and whole-library SUM(fs_size_bytes)
+        # are index-only scans that never touch the wide roms rows
+        Index("idx_roms_platform_fs_size", "platform_id", "fs_size_bytes"),
         Index("idx_roms_name", "name"),
         Index("idx_roms_name_sort_key", "name_sort_key"),
         Index("idx_roms_igdb_id", "igdb_id"),