Server wrongly used as reader for Galera cluster with 'writer_is_also_reader=2'

[JavierJF]

• A clear description of the issue

A server is wrongly placed in the reader_hostgroup for writer_is_also_reader=2 when there are no backup servers available.

• ProxySQL version

• v2.0.16

• v2.1.0

• OS version

NAME="Arch Linux"
PRETTY_NAME="Arch Linux"
ID=arch
BUILD_ID=rolling

• The steps to reproduce the issue

1. Configure ProxySQL with the following mysql_galera_hostgroups and mysql_servers configuration:

   mysql> select * from runtime_mysql_galera_hostgroups;
   +------------------+-------------------------+------------------+-------------------+--------+-------------+-----------------------+-------------------------+---------+
   | writer_hostgroup | backup_writer_hostgroup | reader_hostgroup | offline_hostgroup | active | max_writers | writer_is_also_reader | max_transactions_behind | comment |
   +------------------+-------------------------+------------------+-------------------+--------+-------------+-----------------------+-------------------------+---------+
   | 20               | 30                      | 10               | 40                | 1      | 1           | 2                     | 100                     | NULL    |
   +------------------+-------------------------+------------------+-------------------+--------+-------------+-----------------------+-------------------------+---------+
   1 row in set (0.00 sec)
   

   mysql> select * from mysql_servers;
   +--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
   | hostgroup_id | hostname    | port | gtid_port | status | weight | compression | max_connections | max_replication_lag | use_ssl | max_latency_ms | comment |
   +--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
   | 10           | 172.18.1.11 | 3306 | 0         | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
   | 10           | 172.18.1.12 | 3306 | 0         | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
   +--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
   2 rows in set (0.00 sec)
   

2. Configure server 172.18.1.11 read only with: SET GLOBAL read_only=ON;

3. Start ProxySQL.

4. Check that the current writer is in the reader hostgroup, when only one server should be present.

   mysql> select * from runtime_mysql_servers;
   +--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
   | hostgroup_id | hostname    | port | gtid_port | status | weight | compression | max_connections | max_replication_lag | use_ssl | max_latency_ms | comment |
   +--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
   | 10           | 172.18.1.11 | 3306 | 0         | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
   | 20           | 172.18.1.12 | 3306 | 0         | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
   | 10           | 172.18.1.12 | 3306 | 0         | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
   +--------------+-------------+------+-----------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
   3 rows in set (0.00 sec)
   

• The full ProxySQL error log (default location: /var/lib/proxysql/proxysql.log)

Attached can be found:

• Full ProxySQL error log during the issue reproduction.
• mysql_servers table configuration.
• galera_hostgroups table configuration.
• Final runtime_mysql_servers state.

extra_reader_wiar_two.tar.gz