Slow Performance for some queries

Hi there,

I have discovered some very low performing queries on our MariaDB version 5.3.7. The query shows up with "string results in query cache"

The query:

explain select distinct
        `config`.`agent_id` AS `agent_id`,
        `config`.`agent_name` AS `agent_name`,
        `agent`.`agent_version` AS `agent_version`,
        `config`.`agent_os` AS `agent_os`,
        `agent`.`agent_os_version` AS `agent_os_version`,
        `config`.`pconfig_line` AS `pconfig_line`,
        `config`.`appclass` AS `appclass`,
        `config`.`instance` AS `instance`,
        `config`.`parameter` AS `parameter`,
        `config`.`value` AS `value`,
        substring_index(substring_index(`config`.`variable`, '/', '4ö'),
                '/',
                -(1)) AS `NT_Drive`,
        `config`.`agent_config_date` AS `agent_config_date`,
        `config`.`rule_type_name` AS `rule_type_name`
    from
        (`agent_config_detail_view` `config`
        left join `agent` ON ((`agent`.`agent_id` = `config`.`agent_id`)))
    where
        (((`config`.`rule_type_id` = 'ccbe914e30c6ec6e3aa5c4780a3525d6')
            or (`config`.`rule_type_id` = '0091efee7f9b5f0e27211eb7226d0a23')
            or (`config`.`rule_type_id` = '6311ae17c1ee52b36e68aaf4ad066387'))
            and ((`config`.`variable` = '/AgentSetup/FILESYSTEM.filterList')
            or (`config`.`variable` = '/AgentSetup/FILESYSTEM.filterType')
            or (`config`.`variable` like '/AS/EVENTSPRING/PARAM_SETTINGS/THRESHOLDS/FILESYSTEM%')
            or (`config`.`variable` like '/RecoveryActions/NT_LOGICAL_DISKS/%/LDldFreeSpacePercent/Mode'))
            and (`config`.`agent_config_date` > ((select 
                max(`s`.`agent_config_date`)
            from
                `agent_config` `s`) - interval 24 hour)))
    order by `config`.`agent_name` , `config`.`appclass`

Here is the explain for the query in question:

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	a	ALL	PRIMARY	NULL	NULL	NULL	7083	"Using temporary; Using filesort"
1	PRIMARY	agent	eq_ref	PRIMARY	PRIMARY	34	new_budm.a.agent_id	1	
1	PRIMARY	b	ref	PRIMARY,fk_agent_config_agent1,IX_agent_config_date	fk_agent_config_agent1	34	new_budm.a.agent_id	3	"Using where"
1	PRIMARY	c	ref	agent_config_rule_fk_agent_config_id,agent_config_rule_fk_rule_id	agent_config_rule_fk_agent_config_id	34	new_budm.b.agent_config_id	947	
1	PRIMARY	d	eq_ref	PRIMARY,IX_rule_variable	PRIMARY	34	new_budm.c.fk_rule_id	1	"Using where"
1	PRIMARY	e	ref	fk_rule_rule_type_rule_type1,fk_rule_rule_type_rule	fk_rule_rule_type_rule	34	new_budm.c.fk_rule_id	1	"Using where"
1	PRIMARY	f	eq_ref	PRIMARY	PRIMARY	34	new_budm.e.fk_rule_type_id	1	
2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	"Select tables optimized away"

The query cache (innodb_buffer_pool_size) is set to 8192M.

Other queries are running fine (perfomance can always be better).

Thank you and regards, Patrick