@@ -175,6 +175,7 @@ migrations_added:
 # Migration tests only exercise migrations, so PRs only run them when these change.
 migration_tests:
   - '.github/workflows/backend.yml'
+  - '.github/workflows/scripts/migration-test-db.py'
   - 'Makefile'
   - 'src/**/migrations/**'
   - 'tests/**/migrations/**'
 
@@ -369,6 +369,9 @@ jobs:
       contents: read
       actions: read
       pull-requests: write
+    env:
+      MIGRATION_DB_DIR: .artifacts/migration-test-db
+      SAVE_MIGRATION_DB: ${{ github.ref == 'refs/heads/master' }}
 
     steps:
       - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
@@ -379,10 +382,33 @@ jobs:
         with:
           mode: default
 
+      # Only master saves, so PRs restore the newest master dump.
+      - name: Restore migrated test databases
+        id: db-cache
+        uses: actions/cache/restore@1bd1e32a3bdc45362d1e726936510720a7c30a57 # v4.2.0
+        with:
+          path: ${{ env.MIGRATION_DB_DIR }}
+          key: migration-test-db-v1-${{ hashFiles('src/**/migrations/*.py', 'src/sentry/new_migrations/**/*.py') }}
+          restore-keys: migration-test-db-v1-
+
+      - name: Load migrated test databases
+        run: .github/workflows/scripts/migration-test-db.py restore "$MIGRATION_DB_DIR"
+
       - name: run tests
         run: |
           make test-migrations-ci
 
+      - name: Dump migrated test databases
+        if: env.SAVE_MIGRATION_DB == 'true' && steps.db-cache.outputs.cache-hit != 'true'
+        run: .github/workflows/scripts/migration-test-db.py save "$MIGRATION_DB_DIR"
+
+      - name: Save migrated test databases
+        if: env.SAVE_MIGRATION_DB == 'true' && steps.db-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@1bd1e32a3bdc45362d1e726936510720a7c30a57 # v4.2.0
+        with:
+          path: ${{ env.MIGRATION_DB_DIR }}
+          key: ${{ steps.db-cache.outputs.cache-primary-key }}
+
       - name: Report failures
         if: ${{ !cancelled() && github.event_name == 'pull_request' }}
         continue-on-error: true
 
@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+"""Save and restore the migrated test databases used by the migration tests.
+
+With --reuse-db, pytest keeps a restored database and only applies the
+migrations added since it was dumped, instead of running every migration.
+
+Usage: migration-test-db.py save|restore DIR
+"""
+
+from __future__ import annotations
+
+import subprocess
+import sys
+from pathlib import Path
+from typing import BinaryIO
+
+POSTGRES_CONTAINER = "postgres-postgres-1"
+POSTGRES_USER = "postgres"
+# Django's test names for the region, control and secondary databases.
+TEST_DATABASES = ("test_region", "test_control", "test_secondary")
+MIGRATION_GLOB = "src/**/migrations/*.py"
+MANIFEST = "migrations.txt"
+
+REPO_ROOT = Path(__file__).resolve().parents[3]
+
+
+def migration_files() -> set[str]:
+    return {str(p.relative_to(REPO_ROOT)) for p in REPO_ROOT.glob(MIGRATION_GLOB)}
+
+
+def postgres(*args: str, stdin: BinaryIO | None = None, stdout: BinaryIO | None = None) -> None:
+    subprocess.run(
+        ["docker", "exec", "-i", POSTGRES_CONTAINER, *args], check=True, stdin=stdin, stdout=stdout
+    )
+
+
+def save(cache_dir: Path) -> None:
+    cache_dir.mkdir(parents=True, exist_ok=True)
+    for db in TEST_DATABASES:
+        with open(cache_dir / f"{db}.dump", "wb") as f:
+            postgres("pg_dump", "-U", POSTGRES_USER, "--format=custom", db, stdout=f)
+    (cache_dir / MANIFEST).write_text("\n".join(sorted(migration_files())))
+
+
+def restore(cache_dir: Path) -> None:
+    manifest = cache_dir / MANIFEST
+    if not manifest.is_file():
+        print("No saved databases; pytest will build them.")
+        return
+
+    # A dump with migrations this checkout lacks (e.g. a branch behind master)
+    # can't be migrated forward, so build from scratch instead.
+    missing = set(manifest.read_text().split()) - migration_files()
+    if missing:
+        print(f"Saved databases include {len(missing)} unknown migrations; pytest will build them.")
+        return
+
+    for db in TEST_DATABASES:
+        postgres("createdb", "-U", POSTGRES_USER, db)
+        with open(cache_dir / f"{db}.dump", "rb") as f:
+            postgres("pg_restore", "-U", POSTGRES_USER, "--dbname", db, stdin=f)
+
+
+def main() -> None:
+    commands = {"save": save, "restore": restore}
+    if len(sys.argv) != 3 or sys.argv[1] not in commands:
+        sys.exit(__doc__)
+    commands[sys.argv[1]](Path(sys.argv[2]))
+
+
+if __name__ == "__main__":
+    main()