Log tracer errors (#6066)

Example (would log several times if not for the helper fn. Would emit no
logs due to mulithreading previously)

![image](https://github.com/hwchase17/langchain/assets/130414180/070d25ae-1f06-4487-9617-0a6f66f3f01e)

langchain/callbacks/tracers/langchain.py

@@ -16,6 +16,16 @@
 from langchain.schema import BaseMessage, messages_to_dict
 
 logger = logging.getLogger(__name__)
+_LOGGED = set()
+
+
+def log_error_once(method: str, exception: Exception) -> None:
+    """Log an error once."""
+    global _LOGGED
+    if (method, type(exception)) in _LOGGED:
+        return
+    _LOGGED.add((method, type(exception)))
+    logger.error(exception)
 
 
 class LangChainTracer(BaseTracer):
@@ -76,11 +86,21 @@ def _persist_run_single(self, run: Run) -> None:
         extra = run_dict.get("extra", {})
         extra["runtime"] = get_runtime_environment()
         run_dict["extra"] = extra
-        run = self.client.create_run(**run_dict, session_name=self.session_name)
+        try:
+            run = self.client.create_run(**run_dict, session_name=self.session_name)
+        except Exception as e:
+            # Errors are swallowed by the thread executor so we need to log them here
+            log_error_once("post", e)
+            raise
 
     def _update_run_single(self, run: Run) -> None:
         """Update a run."""
-        self.client.update_run(run.id, **run.dict())
+        try:
+            self.client.update_run(run.id, **run.dict())
+        except Exception as e:
+            # Errors are swallowed by the thread executor so we need to log them here
+            log_error_once("patch", e)
+            raise
 
     def _on_llm_start(self, run: Run) -> None:
         """Persist an LLM run."""