do not clear the pool on SystemOverloaded

Author: blink1073

pymongo/asynchronous/topology.py

@@ -890,7 +890,9 @@ async def _handle_error(self, address: _Address, err_ctx: _ErrorContext) -> None
                 # Clear the pool.
                 await server.reset(service_id)
         elif isinstance(error, ConnectionFailure):
-            if isinstance(error, WaitQueueTimeoutError):
+            if isinstance(error, WaitQueueTimeoutError) or error.has_error_label(
+                "SystemOverloaded"
+            ):
                 return
             # "Client MUST replace the server's description with type Unknown
             # ... MUST NOT request an immediate check of the server."

pymongo/synchronous/topology.py

@@ -888,7 +888,9 @@ def _handle_error(self, address: _Address, err_ctx: _ErrorContext) -> None:
                 # Clear the pool.
                 server.reset(service_id)
         elif isinstance(error, ConnectionFailure):
-            if isinstance(error, WaitQueueTimeoutError):
+            if isinstance(error, WaitQueueTimeoutError) or error.has_error_label(
+                "SystemOverloaded"
+            ):
                 return
             # "Client MUST replace the server's description with type Unknown
             # ... MUST NOT request an immediate check of the server."