MySQL inserts/deletes slowing down after a while after Start/Reboot

MySQLmysql-5.5

The Setup here is:
OS: Ubuntu 12.04 (1 Core and 1.75 GB of RAMO)
MySQL Version: 5.5

There are about 8 to 9 tables in the database. On initially starting mysql the queries are fast at around 0.05 – 0.10 seconds, however after sometime the INSERTS and DELETES slow down to around 1 – 2 seconds, however the SELECTS are still around 0.05 – 0.10 seconds.

Then after rebooting the system the situation reverts back to how it was in the beginning of the previous paragraph. Everything is fast, but then INSERTS and DELETES slow down tremendously after a while.

Note: I'm just doing simple inserts and deletes on very few records, and the database starts with empty tables in the beginning.

Any insight?

Edit: Create Table of 1 of the Tables

| FeedUps | 
CREATE TABLE `FeedUps` (
  `post_id` int(10) unsigned DEFAULT NULL,
  `liker` int(10) unsigned DEFAULT NULL,
  UNIQUE KEY `post_id` (`post_id`,`liker`),
  KEY `liker` (`liker`),
  CONSTRAINT `FeedUps_ibfk_1` FOREIGN KEY (`post_id`) 
      REFERENCES `Feed` (`post_id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `FeedUps_ibfk_2` FOREIGN KEY (`liker`) 
      REFERENCES `Users` (`user_id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1

Best Answer

I found the problem, in the my.cnf file I had turned on TABLE_CACHE.
The way I resolved it without having to restart it was by using the command FLUSH TABLES. Shortly after that the inserts/updates/deletes resumed working at normal speeds.

Related Solutions

MySQL Replication question

On the slave, you can configure MySQL to skip certain errors by using the slave-skip-errors configuration item.

In the case above, you'd add the following to your my.cnf;

slave-skip-errors = 1452

But I'd be extremely wary about doing this, as the referential integrity is there for a reason, and without it, your slave could not be satisfactorily promoted to take the place of the master in the case of something going wrong with your master hardware...

http://dev.mysql.com/doc/refman/5.5/en/replication-options-slave.html#option_mysqld_slave-skip-errors

Mysql – “Cannot add or update a child row” when deleting a record

On the face of it, that does seem impossible.

The thing is, your error suggests it's not that you're trying to delete at all.

The message you're getting suggests you're trying to insert or update a row in the child table, not delete a row from the parent table. If the foreign key you posted was causing the problem relative to a delete, you should see this message, instead:

Cannot delete or update a parent row: a foreign key constraint fails (`test`.`bar`, CONSTRAINT `bar_ibfk_1` FOREIGN KEY (`foo_id`) REFERENCES `foo` (`id`))

It's also possible you have some BEFORE DELETE trigger magic on survey_main that's doing something unexpected.

Right after this error occurs, try this:

SHOW ENGINE INNODB STATUS;

The LATEST FOREIGN KEY ERROR section should give you something more to go on. Failing that, you could enable the general log, which will show queries executed by triggers and other stored programs, as well as the queries you're directly executing, to shed light on what might be going on behind the scenes.

Update (#1) Things are definitely not as they seem and the full table definitions are going to be pretty critical, here.

Also, the version of MySQL you're using may also be relevant, so please mention it.

With nothing more to go on at the moment, I'm speculating that you have invalid data in the survey_id column of the survey_answers table. To test that theory:

SELECT *
  FROM survey_answers sa
  LEFT JOIN survey_main sm ON sm.id = sa.survey_id
 WHERE sm.id IS NULL;

If I understand your schema correctly, then this query will return zero rows if I am wrong. :) If you get rows returned, then those rows have survey_answers records that contain an survey_id value that doesn't exist in the id column of survey_main.

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