Mysql LOAD DATA INFILE - getting slower and slower

Question

Setup: MyISAM table with 8 columns... and there's 1 index on a column. No foreign keys.

Data: Inserting 500m+ records via Pymysql / LOAD data

Server: Mariadb 10.08 on a VPS with 1gb RAM (yeah I know.. client's server, not mine)

Schema:

drop table if exists profiles;
create table profiles (
    id          bigint auto_increment primary key,
    first_name  varchar(128) NULL,
    last_name   varchar(128) NULL,
    liid        varchar(256) NOT NULL,
    city        varchar(128) NULL,
    state       varchar(128) NULL,
    country     varchar(128) NULL,
    email       varchar(512) null,
    phone       varchar(512) null
) engine=MyISAM auto_increment=0 default CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
create index liid_idx on profiles(liid);

I'm loading 1m records at a time. Here's some code:

connection = None 
cursor = None

def execute_sql( sql ):
    global cursor
    cursor.execute( sql )
    
def open_db(mysql_user, mysql_passwd, mysql_host, mysql_db):
    global connection, cursor
    connection = MySQLdb.Connect(host=mysql_host, user=mysql_user, passwd=mysql_passwd, db=mysql_db, local_infile=True)
    cursor = connection.cursor()

    ########################################################################################
    # https://stackoverflow.com/questions/2463602/mysql-load-data-infile-acceleration
    #
    # note: this must be run as root
    ########################################################################################

    cursor.execute("set autocommit = 0;");
    cursor.execute("set unique_checks = 0;");
    cursor.execute("set foreign_key_checks = 0;");
    cursor.execute("set sql_log_bin = 0;");


def close_db():
    global connection
    connection.commit()




open_db(
        mysql_user=mysql_user,
        mysql_passwd=mysql_passwd,
        mysql_host=mysql_host,
        mysql_db=mysql_db
    )

for file in [....]:
    start = time.time()

    execute_sql(sql='''
    LOAD DATA LOCAL INFILE '{}' INTO TABLE profile FIELDS TERMINATED by '\t' ENCLOSED BY '"' (@first_name, @last_name, liid, @city, @state, @country, @email, @phone) SET first_name = NULLIF(@first_name,''), first_name = NULLIF(@first_name,''), last_name = NULLIF(@last_name,''), city = NULLIF(@city,''), state = NULLIF(@state,''), country = NULLIF(@country,''), email = NULLIF(@email,''), phone = NULLIF(@phone,'');
    '''.format(file))

    end = time.time()

    duration= end-start

    print("[mysql] duration: {} seconds".format(int(duration))

close_db()

It's getting slower and slower.

Any ideas?

Results:

[mysql] duration:26 seconds

[mysql] duration:63 seconds

[mysql] duration:73 seconds

[mysql] duration:75 seconds

[mysql] duration:81 seconds

[mysql] duration:91 seconds

[mysql] duration:85 seconds

[mysql] duration:94 seconds

[mysql] duration:98 seconds

[mysql] duration:96 seconds

[mysql] duration:107 seconds

[mysql] duration:122 seconds

[mysql] duration:141 seconds

[mysql] duration:169 seconds

[mysql] duration:255 seconds

[mysql] duration:356 seconds

[mysql] duration:822 seconds

[mysql] duration:1590 seconds

[mysql] duration:2454 seconds

[mysql] duration:3800 seconds

[mysql] duration:4080 seconds

[mysql] duration:4459 seconds

[mysql] duration:4879 seconds

[mysql] duration:4638 seconds

[mysql] duration:4994 seconds

[mysql] duration:5749 seconds

[mysql] duration:5047 seconds

[mysql] duration:5641 seconds

[mysql] duration:6207 seconds

[mysql] duration:6325 seconds

[mysql] duration:6772 seconds