perf: chain db transactions (#33004)

* perf: chain transactions

Frequently used rollback/commits can be modified to chain previous
transaction.

This reduces one query to DB in most requests.

* perf: chain transactions in requests

frappe/app.py

@@ -128,7 +128,7 @@ def application(request: Request):
 	except Exception as e:
 		response = e.get_response(request.environ) if isinstance(e, HTTPException) else handle_exception(e)
 		if db := getattr(frappe.local, "db", None):
-			db.rollback()
+			db.rollback(chain=True)
 
 	else:
 		sync_database()
@@ -398,9 +398,9 @@ def sync_database():
 
 	# if HTTP method would change server state, commit if necessary
 	if frappe.local.request.method in UNSAFE_HTTP_METHODS or frappe.local.flags.commit:
-		db.commit()
+		db.commit(chain=True)
 	else:
-		db.rollback()
+		db.rollback(chain=True)
 
 	# update session
 	if session := getattr(frappe.local, "session_obj", None):

frappe/database/database.py

@@ -1147,7 +1147,7 @@ class Database:
 		mode = "READ ONLY" if read_only else ""
 		self.sql(f"START TRANSACTION {mode}")
 
-	def commit(self):
+	def commit(self, *, chain=False):
 		"""Commit current transaction. Calls SQL `COMMIT`."""
 		if self._disable_transaction_control:
 			warnings.warn(message=TRANSACTION_DISABLED_MSG, stacklevel=2)
@@ -1158,12 +1158,15 @@ class Database:
 
 		self.before_commit.run()
 
-		self.sql("commit")
-		self.begin()  # explicitly start a new transaction
+		if chain:
+			self.sql("commit and chain")
+		else:
+			self.sql("commit")
+			self.begin()
 
 		self.after_commit.run()
 
-	def rollback(self, *, save_point=None):
+	def rollback(self, *, save_point=None, chain=False):
 		"""`ROLLBACK` current transaction. Optionally rollback to a known save_point."""
 		if save_point:
 			self.sql(f"rollback to savepoint {save_point}")
@@ -1173,8 +1176,11 @@ class Database:
 
 			self.before_rollback.run()
 
-			self.sql("rollback")
-			self.begin()
+			if chain:
+				self.sql("rollback and chain")
+			else:
+				self.sql("rollback")
+				self.begin()
 
 			self.after_rollback.run()
 		else:

frappe/utils/background_jobs.py

@@ -272,7 +272,7 @@ def execute_job(site, method, event, job_name, kwargs, user=None, is_async=True,
 		retval = method(**kwargs)
 
 	except (frappe.db.InternalError, frappe.RetryBackgroundJobError) as e:
-		frappe.db.rollback()
+		frappe.db.rollback(chain=True)
 
 		if retry < 5 and (
 			isinstance(e, frappe.RetryBackgroundJobError)
@@ -293,15 +293,15 @@ def execute_job(site, method, event, job_name, kwargs, user=None, is_async=True,
 			raise
 
 	except Exception as e:
-		frappe.db.rollback()
+		frappe.db.rollback(chain=True)
 		frappe.log_error(title=method_name)
 		frappe.monitor.add_data_to_monitor(exception=e.__class__.__name__)
-		frappe.db.commit()
+		frappe.db.commit(chain=True)
 		print(frappe.get_traceback())
 		raise
 
 	else:
-		frappe.db.commit()
+		frappe.db.commit(chain=True)
 		return retval
 
 	finally: