feat: support countig till a limit

In InnoDB counting is essentially O(n) operation, it can be pretty fast
on indexes but when filters don't use any index it usually means doing a
full table scan.

Adding a limit will stop the scan as soon as that many records are
matched.

frappe/desk/reportview.py

@@ -52,14 +52,24 @@ def get_count() -> int:
 
 	if is_virtual_doctype(args.doctype):
 		controller = get_controller(args.doctype)
-		data = frappe.call(controller.get_count, args=args, **args)
+		count = frappe.call(controller.get_count, args=args, **args)
 	else:
 		args.distinct = sbool(args.distinct)
 		distinct = "distinct " if args.distinct else ""
-		args.fields = [f"count({distinct}`tab{args.doctype}`.name) as total_count"]
-		data = execute(**args)[0].get("total_count")
+		args.limit = cint(args.limit)
+		if args.limit:
+			# Only "count until this limit"
+			args.fields = ["*"]
+			partial_query = execute(**args, run=0)
+			count = frappe.db.sql(
+				f"""with records as ( {partial_query} )
+					select count(*) from records""",
+			)[0][0]
+		else:
+			args.fields = [f"count({distinct}`tab{args.doctype}`.name) as total_count"]
+			count = execute(**args)[0].get("total_count")
 
-	return data
+	return count
 
 
 def execute(doctype, *args, **kwargs):

frappe/public/js/frappe/db.js

@@ -96,6 +96,7 @@ frappe.db = {
 	},
 	count: function (doctype, args = {}) {
 		let filters = args.filters || {};
+		let limit = args.limit;
 
 		// has a filter with childtable?
 		const distinct =
@@ -111,6 +112,7 @@ frappe.db = {
 			filters,
 			fields,
 			distinct,
+			limit,
 		});
 	},
 	get_link_options(doctype, txt = "", filters = {}) {

frappe/public/js/frappe/list/list_view.js

@@ -946,6 +946,7 @@ frappe.views.ListView = class ListView extends frappe.views.BaseList {
 		return frappe.db
 			.count(this.doctype, {
 				filters: this.get_filters_for_args(),
+				limit: 1001,
 			})
 			.then((total_count) => {
 				this.total_count = total_count || current_count;

frappe/tests/test_db_query.py

@@ -1187,7 +1187,7 @@ def test_get_count(self):
 				"distinct": "false",
 			}
 		)
-		list_filter_response = execute_cmd("frappe.desk.reportview.get_count")
+		count = execute_cmd("frappe.desk.reportview.get_count")
 		frappe.local.form_dict = frappe._dict(
 			{
 				"doctype": "DocType",
@@ -1196,8 +1196,8 @@ def test_get_count(self):
 			}
 		)
 		dict_filter_response = execute_cmd("frappe.desk.reportview.get_count")
-		self.assertIsInstance(list_filter_response, int)
-		self.assertEqual(list_filter_response, dict_filter_response)
+		self.assertIsInstance(count, int)
+		self.assertEqual(count, dict_filter_response)
 
 		# test with child table filter
 		frappe.local.form_dict = frappe._dict(
@@ -1218,6 +1218,21 @@ def test_get_count(self):
 		)[0][0]
 		self.assertEqual(child_filter_response, current_value)
 
+		# test with limit
+		limit = 2
+		frappe.local.form_dict = frappe._dict(
+			{
+				"doctype": "DocType",
+				"filters": [["DocType", "is_virtual", "=", 1]],
+				"fields": [],
+				"distinct": "false",
+				"limit": limit,
+			}
+		)
+		count = execute_cmd("frappe.desk.reportview.get_count")
+		self.assertIsInstance(count, int)
+		self.assertLessEqual(count, limit)
+
 	def test_reportview_get(self):
 		user = frappe.get_doc("User", "test@example.com")
 		add_child_table_to_blog_post()