Grotesque memory usage and leaks with flask-sqlalchemy on Debian Wheezy

I am making a simple web application that pulls (currently over 64000 fields in two tables and grows) data from a MySQL database using flask-sqlalchemy. I only ran one instance and did not notice any problems until I ran out of RAM and the thing stopped. I understand that

I might have to rethink how it all works since I can't keep adding RAM (it's a small VM, so I'm 512 to 768 MB, but still) ... but depressing Python should free up memory after processing the request ? Indeed, when running the same flash app on my Windows machine, it sucks up RAM (but only half as much!) And when it's done, it's freed up. Not so on a Debian machine that runs a lot of (supposedly) tiny applications. As far as I know, the lib versions running on both machines are the same. The Debian machine even has a later version of Python than the Windows machine. They both connect to the same database. How can I proceed?

from flask import Flask, request, jsonify
from flask.ext.sqlalchemy import SQLAlchemy

import re
from datetime import datetime

app = Flask(__name__)
app.config.from_pyfile('settings.cfg')
db = SQLAlchemy(app)

class Reports(db.Model):
    __tablename__ = 'reports'

    id          = db.Column(db.Integer, primary_key=True)
    ip          = db.Column(db.Integer)
    date        = db.Column(db.DateTime)
    sid         = db.Column(db.Integer)
    version     = db.Column(db.Integer)
    itemname    = db.Column(db.String(25))
    group       = db.Column(db.Integer)
    pclass      = db.Column(db.String(15))
    ltime       = db.Column(db.Integer)
    rlen        = db.Column(db.Integer)
    total       = db.Column(db.Integer)

    def __init__(self, pd):
        self.date = datetime.utcnow()
        self.sid = pd["sid"]
        self.version = pd["version"]
        self.itemname = pd["itemname"]
        self.group = pd["group"]
        self.pclass = pd["pclass"]
        self.ltime = pd["ltime"]
        self.rlen = pd["rlen"]
        self.total = pd["total"]


class Perfdata(db.Model):
    __tablename__ = 'perfdata'

    reportid    = db.Column(db.Integer, db.ForeignKey('reports.id'), primary_key=True)
    l70 = db.Column(db.Integer)
    l65 = db.Column(db.Integer)
    l60 = db.Column(db.Integer)
    l55 = db.Column(db.Integer)
    l50 = db.Column(db.Integer)
    l45 = db.Column(db.Integer)
    l40 = db.Column(db.Integer)
    l35 = db.Column(db.Integer)
    l30 = db.Column(db.Integer)

    def __init__(self, reportid, pd):
        self.reportid = reportid
        self.l70 = pd["l70"]
        self.l65 = pd["l65"]
        self.l60 = pd["l60"]
        self.l55 = pd["l55"]
        self.l50 = pd["l50"]
        self.l45 = pd["l45"]
        self.l40 = pd["l40"]
        self.l35 = pd["l35"]
        self.l30 = pd["l30"]

    def buildlist(self):
        plist = []

        plist.append(self.l70)
        plist.append(self.l65)
        plist.append(self.l60)
        plist.append(self.l55)
        plist.append(self.l50)
        plist.append(self.l45)
        plist.append(self.l40)
        plist.append(self.l35)
        plist.append(self.l30)

        return plist


@app.route('/ps', methods=['GET'])
def perfget():

    response = []

    for report, perf in db.session.query(Reports, Perfdata).all():

        response.append("")

        response.append("%s %s %s %s %s %s %s %s" % (report.version,
                                                     report.sid,
                                                     report.itemname,
                                                     report.group,
                                                     report.pclass,
                                                     report.ltime,
                                                     report.rlen,
                                                     report.total))

        response.append("%s %s %s %s %s %s %s %s %s" % (perf.l70,
                                                     perf.l65,
                                                     perf.l60,
                                                     perf.l55,
                                                     perf.l50,
                                                     perf.l45,
                                                     perf.l40,
                                                     perf.l35,
                                                     perf.l30))

    return '<br>\n'.join(response)


if __name__ == '__main__':
    app.run()