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# Overview
MySQL is a fast, stable and true multi-user, multi-threaded SQL database server.
SQL (Structured Query Language) is the most popular database query language in
the world. The main goals of MySQL are speed, robustness and ease of use.
Percona is fork of MySQL by Percona Inc. which focuses on maximizing
performance, particularly for heavy workloads. It is a drop-in replacement for
MySQL and features XtraDB, a drop-in replacement for the InnoDB storage engine.
[http://www.mysql.com](http://www.mysql.com)
[http://www.percona.com/software/percona-server](http://www.percona.com/software/percona-server)
# Usage
## General
To deploy a MySQL service:
juju deploy mysql
Once deployed, you can ssh into the deployed service and access the
MySQL console as the MySQL root user:
juju ssh <unit>
mysql -u root -p
# enter root password - /var/lib/juju/mysql.passwd
To change deployment to a Percona server:
juju set mysql flavor=percona
## Optimization
You can tweak various options to optimize your MySQL deployment:
* max-connections - Maximum connections allowed to server or '-1' for default.
* preferred-storage-engine - A comma separated list of storage engines to
optimize for. First in the list is marked as default storage engine. 'InnoDB'
or 'MyISAM' are acceptable values.
* tuning-level - Specify 'safest', 'fast' or 'unsafe' to choose required
transaction safety. This option determines the flush value for innodb commit
and binary logs. Specify 'safest' for full ACID compliance. 'fast' relaxes the
compliance for performance and 'unsafe' will remove most restrictions.
* dataset-size - Memory allocation for all caches (InnoDB buffer pool, MyISAM
key, query). Suffix value with 'K', 'M', 'G' or 'T' to indicate unit of
kilobyte, megabyte, gigabyte or terabyte respectively. Suffix value with '%'
to use percentage of machine's total memory.
* query-cache-type - Specify 'ON', 'DEMAND' or 'OFF' to turn query cache on,
selectively (dependent on queries) or off.
* query-cache-size - Size of query cache (no. of bytes) or '-1' to use 20%
of memory allocation.
Each of these can be applied by running:
juju set <service> <option>=<value>
e.g.
juju set mysql preferred-storage-engine=InnoDB
juju set mysql dataset-size=50%
juju set mysql query-cache-type=ON
juju set mysql query-cache-size=-1
## Replication
MySQL supports the ability to replicate databases to slave instances. This
allows you, for example, to load balance read queries across multiple slaves or
use a slave to perform backups, all whilst not impeding the master's
performance.
To deploy a slave:
# deploy second service
juju deploy mysql mysql-slave
# add master to slave relation
juju add-relation mysql:master mysql-slave:slave
Any changes to the master are reflected on the slave.
Any queries that modify the database(s) should be applied to the master only.
The slave should be treated strictly as read only.
You can add further slaves with:
juju add-unit mysql-slave
## Monitoring
This charm provides relations that support monitoring via either Nagios or
Munin. Refer to the appropriate charm for usage.
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