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Running Multiple MySQL Instances on One Machine

550

Section 4.5.4, “

mysqldump

— A Database Backup Program”

. In addition, the binary log is flushed

when its size reaches the value of the

max_binlog_size

[1472]

system variable.

A log-flushing operation does the following:

• If general query logging (

--log

[411]

) or slow query logging (

--log-slow-queries

[412]

) to a

log file is enabled, the server closes and reopens the general query log file or slow query log file.

• If binary logging (

--log-bin

[1467]

) is used, the server closes the current log file and opens a new

log file with the next sequence number.

• If the server was started with the

--log-error

[411]

option to cause the error log to be written to

a file, it renames the current log file with the suffix

-old

and creates a new empty error log file.

The server creates a new binary log file when you flush the logs. However, it just closes and reopens
the general and slow query log files. To cause new files to be created on Unix, rename the current log
files before flushing them. At flush time, the server opens new log files with the original names. For
example, if the general and slow query log files are named

mysql.log

and

mysql-slow.log

, you

can use a series of commands like this:

shell>

cd mysql-data-directory

shell>

mv mysql.log mysql.old

shell>

mv mysql-slow.log mysql-slow.old

shell>

mysqladmin flush-logs

On Windows, use

rename

rather than

At this point, you can make a backup of

mysql.old

and

mysql-slow.old

and then remove them

from disk.

For older versions of MySQL, you cannot rename certain log files on Windows while the server has
them open. Before MySQL 5.0.17, this restriction applies to all log files. You must stop the server,
rename the file, then restart the server to create a new log file. From 5.0.18 on, the restriction applies
only to the error log file. To rename the error log file, a stop and restart can be avoided by flushing the
logs to cause the server to rename the current log file with the suffix

-old

and create a new empty

error log file.

To disable or enable general query logging for the current connection, set the session

sql_log_off

[494]

variable to

OFF

5.3. Running Multiple MySQL Instances on One Machine

In some cases, you might want to run multiple instances of MySQL on a single machine. You might
want to test a new MySQL release while leaving an existing production setup undisturbed. Or you
might want to give different users access to different

mysqld

servers that they manage themselves.

(For example, you might be an Internet Service Provider that wants to provide independent MySQL
installations for different customers.)

It is possible to use a different MySQL server binary per instance, or use the same binary for multiple
instances, or any combination of the two approaches. For example, you might run a server from
MySQL 4.1 and one from MySQL 5.0, to see how different versions handle a given workload. Or
you might run multiple instances of the current production version, each managing a different set of
databases.

Whether or not you use distinct server binaries, each instance that you run must be configured with
unique values for several operating parameters. This eliminates the potential for conflict between
instances. Parameters can be set on the command line, in option files, or by setting environment
variables. See

Section 4.2.3, “Specifying Program Options”

. To see the values used by a given

instance, connect to it and execute a

SHOW VARIABLES

statement.

The primary resource managed by a MySQL instance is the data directory. Each instance should use
a different data directory, the location of which is specified using the

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