From 74df61400793f2a66355541de8f2103a1f457346 Mon Sep 17 00:00:00 2001 From: Baptiste Jonglez Date: Sun, 1 Jan 2017 21:17:47 +0100 Subject: [PATCH] Optimise SQL queries when displaying bills for a project By defaut, SQLAlchemy uses lazy loading, which means that displaying n bills will generate around n queries (to get the list of owers of each bill). Pre-load the list of owers to drastically decrease the number of SQL queries. Before this commit: 1004 SQL queries, 7535 ms elapsed time, 7536 ms CPU time, 530 ms SQL time After this commit: 5 SQL queries, 3342 ms elapsed time, 3393 ms CPU time, 15 ms SQL time Measured request: display the list of all bills for the project (without displaying the sidebar with balances) Test setup to measure performance improvement: - 5 users with various weights - 1000 bills, each paid by a random user, each involving all 5 users - laptop with Celeron N2830@2.16 GHz, SSD Samsung 850 EVO - sqlite database on SSD, using sqlite 3.15.2 - python 2.7.13 - Flask-DebugToolbar 0.10.0 (to count SQL queries and loading time) Performance measurements (using Flask-DebugToolbar with the second request, to avoid measuring cold-cache performance): - number of SQL queries - elapsed time (from request to response) - total CPU time consumed by the server handling the request - total time spent on SQL queries (as reported by SQLAlchemy) --- budget/web.py | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/budget/web.py b/budget/web.py index 63fbe4d..87aef26 100644 --- a/budget/web.py +++ b/budget/web.py @@ -15,6 +15,7 @@ from flask.ext.mail import Mail, Message from flask.ext.babel import get_locale, gettext as _ from smtplib import SMTPRecipientsRefused import werkzeug +from sqlalchemy import orm # local modules from models import db, Project, Person, Bill @@ -277,7 +278,8 @@ def list_bills(): # set the last selected payer as default choice if exists if 'last_selected_payer' in session: bill_form.payer.data = session['last_selected_payer'] - bills = g.project.get_bills() + # Preload the "owers" relationship for all bills + bills = g.project.get_bills().options(orm.subqueryload(Bill.owers)) return render_template("list_bills.html", bills=bills, member_form=MemberForm(g.project),