Fix: task limiter issue. (#7873)

### What problem does this PR solve?

#7869

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/svr/task_executor.py

@@ -103,6 +103,7 @@ MAX_CONCURRENT_MINIO = int(os.environ.get('MAX_CONCURRENT_MINIO', '10'))
 task_limiter = trio.CapacityLimiter(MAX_CONCURRENT_TASKS)
 chunk_limiter = trio.CapacityLimiter(MAX_CONCURRENT_CHUNK_BUILDERS)
 minio_limiter = trio.CapacityLimiter(MAX_CONCURRENT_MINIO)
+kg_limiter = trio.CapacityLimiter(2)
 WORKER_HEARTBEAT_TIMEOUT = int(os.environ.get('WORKER_HEARTBEAT_TIMEOUT', '120'))
 stop_event = threading.Event()
 
@@ -539,8 +540,6 @@ async def do_handle_task(task):
         chunks, token_count = await run_raptor(task, chat_model, embedding_model, vector_size, progress_callback)
     # Either using graphrag or Standard chunking methods
     elif task.get("task_type", "") == "graphrag":
-        global task_limiter
-        task_limiter = trio.CapacityLimiter(2)
         if not task_parser_config.get("graphrag", {}).get("use_graphrag", False):
             return
         graphrag_conf = task["kb_parser_config"].get("graphrag", {})
@@ -548,9 +547,9 @@ async def do_handle_task(task):
         chat_model = LLMBundle(task_tenant_id, LLMType.CHAT, llm_name=task_llm_id, lang=task_language)
         with_resolution = graphrag_conf.get("resolution", False)
         with_community = graphrag_conf.get("community", False)
-        await run_graphrag(task, task_language, with_resolution, with_community, chat_model, embedding_model, progress_callback)
+        async with kg_limiter:
+            await run_graphrag(task, task_language, with_resolution, with_community, chat_model, embedding_model, progress_callback)
         progress_callback(prog=1.0, msg="Knowledge Graph done ({:.2f}s)".format(timer() - start_ts))
-        task_limiter = trio.CapacityLimiter(MAX_CONCURRENT_TASKS)
         return
     else:
         # Standard chunking methods