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Re: New DBA - need some help
Posted by: Rick James
Date: January 12, 2013 11:32AM

> Message=The value of key_cache_disk_writes_ratio is 68.553

Are you using MyISAM? That metric applies to tables using MyISAM Engine. These days, InnoDB is much recommended.

> Message=The value of temp_disk_tables_pct is 32.804

That's one of the dumb metrics. It says "a lot of queries are inefficient", but fails to give any details. I much prefer the SlowLog. It pinpoints the "worst" queries; using a disk-temp-table is just one aspect of "slow". Furthermore, some queries _must_ use disk-temp-tables, so the value is partially bogus.

See the Percona Toolkit. It has, for example, pt-query-digest, which will analyze the slowlog for you.

I have not heard of mysqlautobackup or Grid control, so I cannot address them directly. Pythian group is sharp.

I find that continually monitoring SHOW GLOBAL STATUS and SHOW VARIABLES leads to a very poor signal-to-noise ratio. Even the one I built should not be run more than once or twice.

Back to the SlowLog (my favorite for performance issues)... Find the two worst queries, get the developers to speed them up by 10x (or get rid of them), and performance will be significantly better. Post them here (plus SHOW CREATE TABLE and EXPLAIN); we can help.

As for monitoring Master-Master... SHOW SLAVE STATUS, should say Yes+Yes. If there is a No, then something is wrong. Also, Seconds_behind_master should rarely be more than 1. If it gets big, then SHOW PROCESSLIST (on the Slave) will tell you what is delaying the replication stream; fix it.

You are coming from Oracle, which has a huge number of knobs and whistles. MySQL is much "simpler". Or, you could argue that it is "much dumber". Then, I would counter that complexity begets complexity.

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