fix(db-migrate): enforce gc collection to optimize memory usage

rhodecode/lib/dbmigrate/versions/115_version_5_1_0.py

@@ -35,16 +35,19 b' def downgrade(migrate_engine):'
 
 
 def fixups(models, _SESSION):
+
     for db_repo in _SESSION.query(models.Repository).all():
 
-        config = db_repo._config
-        config.set('extensions', 'largefiles', '')
+        try:
+            config = db_repo._config
+            config.set('extensions', 'largefiles', '')
 
-        try:
-            scm = db_repo.scm_instance(cache=False, config=config)
+            scm = db_repo.scm_instance(cache=False, config=config, vcs_full_cache=False)
             if scm:
                 print(f'installing hook for repo: {db_repo}')
                 scm.install_hooks(force=True)
+            del scm  # force GC
+            del config
         except Exception as e:
             print(e)
             print('continue...')