import mariadb

import resource

db = mariadb.connect(...)

qr = db.cursor()  # doesn't matter if it's buffered or not..

sz = 400

last_id = 0

while True:

    qr.execute('select a, b, c from big_table where id > ? limit ?', (last_id, sz))

    usage = resource.getrusage(resource.RUSAGE_SELF)

    print(f'Mem: {usage[2]}')  # here I'm monitoring how much memory is allocated - It's always a growing number

    rows = qr.fetchall()  # Consume dataset

    last_id += sz

    if len(rows) < sz:

        break