Explicitely give Db connections back to the pool.

So they gracefully release the connection on error instead
of relying on reference-counting to call the Db's `__del__`
(which does not happen in Hypothesis tests) because a ref
to it is kept via the traceback object.

swh/core/db/__init__.py

@@ -113,7 +113,7 @@ class BaseDb:
         self.conn = conn
         self.pool = pool
 
-    def __del__(self):
+    def put_conn(self):
         if self.pool:
             self.pool.putconn(self.conn)
 
@@ -182,6 +182,7 @@ class BaseDb:
                             for k in columns]
                     f.write(','.join(line))
                     f.write('\n')
+
         finally:
             # No problem bubbling up exceptions, but we still need to make sure
             # we finish copying, even though we're probably going to cancel the

swh/core/db/common.py

@@ -43,9 +43,12 @@ def db_transaction(**client_options):
                 return ret
             else:
                 db = self.get_db()
-                with db.transaction() as cur:
-                    apply_options(cur, __client_options)
-                    return meth(self, *args, db=db, cur=cur, **kwargs)
+                try:
+                    with db.transaction() as cur:
+                        apply_options(cur, __client_options)
+                        return meth(self, *args, db=db, cur=cur, **kwargs)
+                finally:
+                    self.put_db(db)
         return _meth
 
     return decorator
@@ -73,8 +76,12 @@ def db_transaction_generator(**client_options):
                 apply_options(cur, old_options)
             else:
                 db = self.get_db()
-                with db.transaction() as cur:
-                    apply_options(cur, __client_options)
-                    yield from meth(self, *args, db=db, cur=cur, **kwargs)
+                try:
+                    with db.transaction() as cur:
+                        apply_options(cur, __client_options)
+                        yield from meth(self, *args, db=db, cur=cur, **kwargs)
+                finally:
+                    self.put_db(db)
+
         return _meth
     return decorator