NXDRIVE-2019: Improve database queries

A small naive benchmark: Direct Transfer a folder containing 100 files.

- Before: ~ 281 req/s
- After:  ~ 352 req/s

From the UX POV, it feels like a significant gain on the overall upload speed.

docs/changes/4.4.5.md

@@ -99,6 +99,8 @@ Release date: `2020-xx-xx`
 - Removed `Engine.get_remote_url()`. Use `server_url` attribute instead.
 - Added `Engine.have_folder_upload`
 - Removed `Engine.remove_staled_transfers()`
+- Added `limit` keyword argument to `EngineDAO.get_dt_uploads_raw()`
+- Changed the return type of `EngineDAO.get_dt_uploads_raw()` from `Generator[Dict[str, Any], None, None]` to `List[Dict[str, Any]]`
 - Removed `Manager.get_tracker_id()`. Use `tracker.uid` attribute instead.
 - Added `username` argument to `QMLDriveApi.update_token()`
 - Removed `QMLDriveApi.get_tracker_id()`

nxdrive/engine/dao/sqlite.py

@@ -9,6 +9,7 @@
 from contextlib import suppress
 from datetime import datetime
 from logging import getLogger
+from os.path import basename
 from pathlib import Path
 from sqlite3 import (
     Connection,
@@ -2246,27 +2247,28 @@ def get_dt_uploads(self) -> Generator[Upload, None, None]:
                 batch=json.loads(res.batch),
             )
 
-    def get_dt_uploads_raw(self) -> Generator[Dict[str, Any], None, None]:
+    def get_dt_uploads_raw(self, limit: int = 1) -> List[Dict[str, Any]]:
         """
         Retrieve all Direct Transfer items.
         Return a simple dict to improve GUI performances (instead of Upload objects).
         """
         con = self._get_read_connection()
         c = con.cursor()
-        for res in c.execute(
-            "SELECT * FROM Uploads WHERE is_direct_transfer = 1"
-        ).fetchall():
-            path = Path(res.path)
-            yield {
+        return [
+            {
                 "uid": res.uid,
-                "name": path.name,
+                "name": basename(res.path),  # More efficient than Path(res.path).name
                 "filesize": res.filesize,
                 "status": TransferStatus(res.status),
                 "engine": res.engine,
                 "progress": res.progress or 0.0,
                 "remote_parent_path": res.remote_parent_path,
                 "remote_parent_ref": res.remote_parent_ref,
             }
+            for res in c.execute(
+                f"SELECT * FROM Uploads WHERE is_direct_transfer = 1 LIMIT {limit}"
+            ).fetchall()
+        ]
 
     def get_downloads_with_status(self, status: TransferStatus) -> List[Download]:
         return [d for d in self.get_downloads() if d.status == status]

nxdrive/gui/api.py

@@ -207,15 +207,8 @@ def get_transfers(self, dao: EngineDAO) -> List[Dict[str, Any]]:
         return result
 
     def get_direct_transfer_items(self, dao: EngineDAO) -> List[Dict[str, Any]]:
-        limit = 5  # 5 files are displayed in the DT window
-        result: List[Dict[str, Any]] = []
-
-        for count, transfer in enumerate(dao.get_dt_uploads_raw()):
-            if count >= limit:
-                break
-            result.append(transfer)
-
-        return result
+        # 5 files are displayed in the DT window
+        return dao.get_dt_uploads_raw(limit=5)
 
     @pyqtSlot(str, str, int, float, bool)
     def pause_transfer(