Refa: revert to original task message collection logic (#8251)

### What problem does this PR solve?

Get rid of 'RedisDB.get_unacked_iterator queue rag_flow_svr_queue_1
doesn't exist'

----

Edit: revert to original message collection logic.

### Type of change

- [x] Refactoring

---------

Co-authored-by: Zhichang Yu <yuzhichang@gmail.com>
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

rag/svr/task_executor.py

@@ -21,8 +21,6 @@ import sys
 import threading
 import time
 
-from valkey import RedisError
-
 from api.utils.log_utils import initRootLogger, get_project_base_directory
 from graphrag.general.index import run_graphrag
 from graphrag.utils import get_llm_cache, set_llm_cache, get_tags_from_cache, set_tags_to_cache
@@ -188,45 +186,20 @@ def set_progress(task_id, from_page=0, to_page=-1, prog=None, msg="Processing...
 async def collect():
     global CONSUMER_NAME, DONE_TASKS, FAILED_TASKS
     global UNACKED_ITERATOR
-    svr_queue_names = get_svr_queue_names()
-    redis_msg = None
 
+    svr_queue_names = get_svr_queue_names()
     try:
         if not UNACKED_ITERATOR:
-            UNACKED_ITERATOR = None
-            logging.debug("Rebuilding UNACKED_ITERATOR due to it is None")
-            try:
-                UNACKED_ITERATOR = REDIS_CONN.get_unacked_iterator(svr_queue_names, SVR_CONSUMER_GROUP_NAME, CONSUMER_NAME)
-                logging.debug("UNACKED_ITERATOR rebuilt successfully")
-            except RedisError as e:
-                UNACKED_ITERATOR = None
-                logging.warning(f"Failed to rebuild UNACKED_ITERATOR: {e}")
-
-        if UNACKED_ITERATOR:
-            try:
-                redis_msg = next(UNACKED_ITERATOR)
-            except StopIteration:
-                UNACKED_ITERATOR = None
-                logging.debug("UNACKED_ITERATOR exhausted, clearing")
-
-            except Exception as e:
-                UNACKED_ITERATOR = None
-                logging.warning(f"UNACKED_ITERATOR raised exception: {e}")
-
-        if not redis_msg:
+            UNACKED_ITERATOR = REDIS_CONN.get_unacked_iterator(svr_queue_names, SVR_CONSUMER_GROUP_NAME, CONSUMER_NAME)
+        try:
+            redis_msg = next(UNACKED_ITERATOR)
+        except StopIteration:
             for svr_queue_name in svr_queue_names:
-                try:
-                    redis_msg = REDIS_CONN.queue_consumer(svr_queue_name, SVR_CONSUMER_GROUP_NAME, CONSUMER_NAME)
-                    if redis_msg:
-                        break
-                except RedisError as e:
-                    logging.warning(f"queue_consumer failed for {svr_queue_name}: {e}")
-                    continue
-
-    except Exception as e:
-        logging.exception(f"collect task encountered unexpected exception: {e}")
-        UNACKED_ITERATOR = None
-        await trio.sleep(1)
+                redis_msg = REDIS_CONN.queue_consumer(svr_queue_name, SVR_CONSUMER_GROUP_NAME, CONSUMER_NAME)
+                if redis_msg:
+                    break
+    except Exception:
+        logging.exception("collect got exception")
         return None, None
 
     if not redis_msg: