Slow InnoDB aggregation queries comparing to Postgresql - mysql

Question

MySQL gurus
We have readonly dataset, which contains around 4 million rows. This dataset is represented as 1 InnoDB table with a bunch of indices, like this:
CREATE TABLE IF NOT EXISTS dim_users (
ds varchar(10),
user_id varchar(32),
date_joined varchar(10),
payer boolean,
source varchar(12),
country varchar(2),
is1dayactive boolean,
is7dayactive boolean,
is28dayactive boolean,
istest boolean
) ENGINE = InnoDB;
ALTER TABLE dim_users ADD INDEX (ds);
ALTER TABLE dim_users ADD INDEX (user_id);
ALTER TABLE dim_users ADD INDEX (date_joined);
ALTER TABLE dim_users ADD INDEX (source);
ALTER TABLE dim_users ADD INDEX (country);
MySQL8 is running on Ubuntu 18.04 in servers.com provider on a cloud server with 8GB of RAM and swap turned off.
The database has default config, except
[mysqld]
innodb-buffer-pool-size=6G
read_only=1
The problem is that aggregation queries like select count(*) from dim_users or select country,count(*) from dim_users group by 1 order by 1 desc; take too much time (up to 12 seconds) comparing to default Postgres 11 setup on the same vhost.
Default psql11 performs the last query for less than 2 seconds.
We were trying to profile and analyze this request on MySQL:
Explain:
mysql> explain analyze select country,count(*) from dim_users group by 1 order by 1 desc;
+---------------+
| EXPLAIN
+---------------+
| -> Group aggregate: count(0) (actual time=241.091..14777.679 rows=11 loops=1)
| -> Index scan on dim_users using country (reverse) (cost=430171.90 rows=4230924) (actual time=0.054..11940.166 rows=4228692 loops=1)
|
+---------------+
1 row in set (14.78 sec)
Profile:
mysql> SELECT SEQ,STATE,DURATION,SWAPS,SOURCE_FUNCTION,SOURCE_FILE,SOURCE_LINE FROM INFORMATION_SCHEMA.PROFILING WHERE QUERY_ID=1;
+-----+--------------------------------+-----------+-------+-------------------------+----------------------+-------------+
| SEQ | STATE | DURATION | SWAPS | SOURCE_FUNCTION | SOURCE_FILE | SOURCE_LINE |
+-----+--------------------------------+-----------+-------+-------------------------+----------------------+-------------+
| 2 | starting | 0.000115 | 0 | NULL | NULL | NULL |
| 3 | Executing hook on transaction | 0.000008 | 0 | launch_hook_trans_begin | rpl_handler.cc | 1119 |
| 4 | starting | 0.000013 | 0 | launch_hook_trans_begin | rpl_handler.cc | 1121 |
| 5 | checking permissions | 0.000010 | 0 | check_access | sql_authorization.cc | 2176 |
| 6 | Opening tables | 0.000050 | 0 | open_tables | sql_base.cc | 5591 |
| 7 | init | 0.000012 | 0 | execute | sql_select.cc | 677 |
| 8 | System lock | 0.000020 | 0 | mysql_lock_tables | lock.cc | 331 |
| 9 | optimizing | 0.000007 | 0 | optimize | sql_optimizer.cc | 282 |
| 10 | statistics | 0.000046 | 0 | optimize | sql_optimizer.cc | 502 |
| 11 | preparing | 0.000035 | 0 | optimize | sql_optimizer.cc | 583 |
| 12 | executing | 13.552128 | 0 | ExecuteIteratorQuery | sql_union.cc | 1409 |
| 13 | end | 0.000037 | 0 | execute | sql_select.cc | 730 |
| 14 | query end | 0.000008 | 0 | mysql_execute_command | sql_parse.cc | 4606 |
| 15 | waiting for handler commit | 0.000018 | 0 | ha_commit_trans | handler.cc | 1589 |
| 16 | closing tables | 0.000015 | 0 | mysql_execute_command | sql_parse.cc | 4657 |
| 17 | freeing items | 0.000039 | 0 | mysql_parse | sql_parse.cc | 5330 |
| 18 | cleaning up | 0.000020 | 0 | dispatch_command | sql_parse.cc | 2184 |
+-----+--------------------------------+-----------+-------+-------------------------+----------------------+-------------+
As you can see, group by query takes ages to complete.
So, my questions are the following.
I've never been using MySQL before, my main DB has always been Postgresql for years and I don't know whether it's normal behaviour for this DB or not - it's very slow when we want to execute group by queries.
Otherwise, if I'm missing something very important here, eg DB or OS configuration, could you please give me a pieces of advice on how to properly setup MySQL for read only purposes.
Thank you!