diff --git a/backend/MediaCacheManager.py b/backend/MediaCacheManager.py
index 20fdd39..67260ae 100644
--- a/backend/MediaCacheManager.py
+++ b/backend/MediaCacheManager.py
@@ -3,6 +3,7 @@ import logging
 import bisect
 import collections
 import asyncio
+import traceback
 import collections
 from typing import Union, Optional
 
@@ -17,7 +18,6 @@ class MediaChunkHolder(object):
     waiters: collections.deque[asyncio.Future]
     requester: list[Request] = []
     chunk_id: int = 0
-    is_done: bool = False
 
     def __init__(self, chat_id: int, msg_id: int, start: int, target_len: int, mem: Optional[bytes] = None) -> None:
         self.chat_id = chat_id
@@ -53,11 +53,6 @@ class MediaChunkHolder(object):
 
     def is_completed(self) -> bool:
         return self.length >= self.target_len
-
-    def set_done(self) -> None:
-        # self.is_done = True
-        # self.notify_waiters()
-        self.requester.clear()
         
     def notify_waiters(self) -> None:
         while self.waiters:
@@ -69,15 +64,15 @@ class MediaChunkHolder(object):
         self.mem = mem
         self.length = len(self.mem)
         if self.length > self.target_len:
-            raise RuntimeWarning(
-                f"MeidaChunk Overflow:start:{self.start},len:{self.length},tlen:{self.target_len}")
+            logger.warning(RuntimeWarning(
+                f"MeidaChunk Overflow:start:{self.start},len:{self.length},tlen:{self.target_len}"))
 
     def append_chunk_mem(self, mem: bytes) -> None:
         self.mem = self.mem + mem
         self.length = len(self.mem)
         if self.length > self.target_len:
-            raise RuntimeWarning(
-                f"MeidaChunk Overflow:start:{self.start},len:{self.length},tlen:{self.target_len}")
+            logger.warning(RuntimeWarning(
+                f"MeidaChunk Overflow:start:{self.start},len:{self.length},tlen:{self.target_len}"))
         self.notify_waiters()
 
     def add_chunk_requester(self, req: Request) -> None:
@@ -85,15 +80,18 @@ class MediaChunkHolder(object):
 
     async def is_disconneted(self) -> bool:
         while self.requester:
-            res = await self.requester[0].is_disconnected()
-            if res:
-                self.requester.pop(0)
-                continue
-            return res
+            req = self.requester[0]
+            if not await req.is_disconnected():
+                return False
+            try:
+                self.requester.remove(req)
+            except Exception as err:
+                logger.warning(f"{err=}, trace:{traceback.format_exc()}")
+                return False
         return True
 
     async def wait_chunk_update(self) -> None:
-        if self.is_done:
+        if self.is_completed():
             return
         waiter = asyncio.Future()
         self.waiters.append(waiter)
diff --git a/backend/TgFileSystemClient.py b/backend/TgFileSystemClient.py
index 97acf8f..4112d36 100644
--- a/backend/TgFileSystemClient.py
+++ b/backend/TgFileSystemClient.py
@@ -21,7 +21,7 @@ logger = logging.getLogger(__file__.split("/")[-1])
 
 class TgFileSystemClient(object):
     MAX_WORKER_ROUTINE = 4
-    SINGLE_NET_CHUNK_SIZE = 256 * 1024  # 256kb
+    SINGLE_NET_CHUNK_SIZE = 512 * 1024  # 512kb
     SINGLE_MEDIA_SIZE = 5 * 1024 * 1024  # 5mb
     api_id: int
     api_hash: str
@@ -245,16 +245,19 @@ class TgFileSystemClient(object):
                 if remain_size <= 0:
                     media_holder.append_chunk_mem(
                         chunk[:len(chunk)+remain_size])
+                else:
+                    media_holder.append_chunk_mem(chunk)
+                if media_holder.is_completed():
                     break
-                media_holder.append_chunk_mem(chunk)
+                if await media_holder.is_disconneted():
+                    raise asyncio.CancelledError("all requester canceled.") 
         except asyncio.CancelledError as err:
-            logger.warning(f"cancel holder:{media_holder}")
+            logger.info(f"cancel holder:{media_holder}")
             self.media_chunk_manager.cancel_media_chunk(media_holder)
         except Exception as err:
             logger.error(
                 f"_download_media_chunk err:{err=},{offset=},{target_size=},{media_holder},\r\n{err=}\r\n{traceback.format_exc()}")
         finally:
-            media_holder.set_done()
             logger.debug(
                 f"downloaded chunk:{time.time()}.{offset=},{target_size=},{media_holder}")
 
@@ -279,7 +282,7 @@ class TgFileSystemClient(object):
                         msg.chat_id, msg.id, align_pos, align_size)
                     holder.add_chunk_requester(req)
                     self.media_chunk_manager.set_media_chunk(holder)
-                    await self.task_queue.put((cur_task_id, self._download_media_chunk(msg, holder)))
+                    self.task_queue.put_nowait((cur_task_id, self._download_media_chunk(msg, holder)))
                 elif not cache_chunk.is_completed():
                     # yield return completed part
                     # await untill completed or pos > end
diff --git a/start.py b/start.py
index 81a3199..6a53aa7 100644
--- a/start.py
+++ b/start.py
@@ -58,4 +58,4 @@ if __name__ == "__main__":
         if ret == 0:
             asyncio.get_event_loop().run_until_complete(run_web_server())
             sys.exit(0)
-    uvicorn.run(backendapp, host="0.0.0.0", port=param.base.port)
+    uvicorn.run(backendapp, host="0.0.0.0", port=param.base.port, app_dir="backend")