Mostly it is linked to the long-query mysql-slow.log records (as you can see mysql-slow.log.text attachments who i posted before) (Most (perhaps all) records corresponding to the time of freezing (long loading))
And freezing are irregular, sometimes among them half hour (sometimes few minutes).
and I attach mysql-slow.log from the time when it happened.
SELECT `mess`.`id` as messageId, `mess`.*, `conv`.* FROM `ow_mailbox_conversation` AS `conv`
INNER JOIN `ow_mailbox_last_message` AS `last_m`
ON (`last_m`.`conversationId` = `conv`.`id`)
INNER JOIN `ow_mailbox_message` AS `mess`
ON ( `last_m`.`initiatorMessageId` = `mess`.id AND ( `last_m`.`initiatorMessageId` > `last_m`.interlocutorMessageId )
OR `last_m`.`interlocutorMessageId` = `mess`.id AND ( `last_m`.`initiatorMessageId` < `last_m`.interlocutorMessageId ) )
WHERE `conv`.`notificationSent` = 0 AND ( ( `conv`.`initiatorId` IN ( '91','3969','691','501','3830','1074','1241','3571','3746','504','3034','3890','2504','3451','117','155','3517','3875','3542','2481','120','2646','2737','635','3924','1020','3033','3828','3894','1477','1997','70','2692','3528','492','3686','3967','2790','597','2391','3780','2421','168','192','3423','3559','3960','166','3047','3974','3921','3975','3231','3966','3944','239','2748','3926','3842','3913','3977','354','1992','3417','3144','2443','260','2014','1622','2396','3437','3516','2973','360','2721','786','500','874','3356','3850','2216','165','3932','3935','3958','3820','3898','916','3055','3786','759','225','3956','2830','3847','3930','3140','2720','2445','1455' ) AND `last_m`.`interlocutorMessageId` > 0 AND `conv`.`deleted` != 1 AND NOT `conv`.`read` & 1 AND NOT `conv`.`viewed` & 1 )
OR ( `conv`.`interlocutorId` IN ( '91','3969','691','501','3830','1074','1241','3571','3746','504','3034','3890','2504','3451','117','155','3517','3875','3542','2481','120','2646','2737','635','3924','1020','3033','3828','3894','1477','1997','70','2692','3528','492','3686','3967','2790','597','2391','3780','2421','168','192','3423','3559','3960','166','3047','3974','3921','3975','3231','3966','3944','239','2748','3926','3842','3913','3977','354','1992','3417','3144','2443','260','2014','1622','2396','3437','3516','2973','360','2721','786','500','874','3356','3850','2216','165','3932','3935','3958','3820','3898','916','3055','3786','759','225','3956','2830','3847','3930','3140','2720','2445','1455' ) AND `conv`.`deleted` != 2 AND NOT `conv`.`read` & 2 AND NOT `conv`.`viewed` & 2 ) );
how often does your cron run?
what is the value for the mails in this constant : const MAIL_COUNT_PER_CRON_JOB = 50; in ow_system_plugins/base/bol/mail_service.php
what is the value for query_execution_time on your server?
2. const MAIL_COUNT_PER_CRON_JOB = 50; (I did not change anything in file mail_service.php)
3. probably i do not understand, where can I find it