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Establishing a Backup Policy

624

the

--log-bin

[1467]

option and that has been running for some days, we find these MySQL binary

log files:

-rw-rw---- 1 guilhem guilhem 1277324 Nov 10 23:59 gbichot2-bin.000001

-rw-rw---- 1 guilhem guilhem 4 Nov 10 23:59 gbichot2-bin.000002

-rw-rw---- 1 guilhem guilhem 79 Nov 11 11:06 gbichot2-bin.000003

-rw-rw---- 1 guilhem guilhem 508 Nov 11 11:08 gbichot2-bin.000004

-rw-rw---- 1 guilhem guilhem 220047446 Nov 12 16:47 gbichot2-bin.000005

-rw-rw---- 1 guilhem guilhem 998412 Nov 14 10:08 gbichot2-bin.000006

-rw-rw---- 1 guilhem guilhem 361 Nov 14 10:07 gbichot2-bin.index

Each time it restarts, the MySQL server creates a new binary log file using the next number in the
sequence. While the server is running, you can also tell it to close the current binary log file and begin
a new one manually by issuing a

FLUSH LOGS

SQL statement or with a

mysqladmin flush-logs

command.

mysqldump

also has an option to flush the logs. The

.index

file in the data directory

contains the list of all MySQL binary logs in the directory.

The MySQL binary logs are important for recovery because they form the set of incremental backups. If
you make sure to flush the logs when you make your full backup, the binary log files created afterward
contain all the data changes made since the backup. Let's modify the previous

mysqldump

command

a bit so that it flushes the MySQL binary logs at the moment of the full backup, and so that the dump
file contains the name of the new current binary log:

shell>

mysqldump --single-transaction --flush-logs --master-data=2 \

--all-databases > backup_sunday_1_PM.sql

After executing this command, the data directory contains a new binary log file,

gbichot2-

bin.000007

, because the

--flush-logs

[300]

option causes the server to flush its logs. The

master-data

[302]

option causes

mysqldump

to write binary log information to its output, so the

resulting

.sql

dump file includes these lines:

-- Position to start replication or point-in-time recovery from

-- CHANGE MASTER TO MASTER_LOG_FILE='gbichot2-bin.000007',MASTER_LOG_POS=4;

Because the

mysqldump

command made a full backup, those lines mean two things:

• The dump file contains all changes made before any changes written to the

gbichot2-

bin.000007

binary log file or newer.

• All data changes logged after the backup are not present in the dump file, but are present in the

gbichot2-bin.000007

binary log file or newer.

On Monday at 1 p.m., we can create an incremental backup by flushing the logs to begin a new
binary log file. For example, executing a

mysqladmin flush-logs

command creates

gbichot2-

bin.000008

. All changes between the Sunday 1 p.m. full backup and Monday 1 p.m. will be in the

gbichot2-bin.000007

file. This incremental backup is important, so it is a good idea to copy it to

a safe place. (For example, back it up on tape or DVD, or copy it to another machine.) On Tuesday
at 1 p.m., execute another

mysqladmin flush-logs

command. All changes between Monday 1

p.m. and Tuesday 1 p.m. will be in the

gbichot2-bin.000008

file (which also should be copied

somewhere safe).

The MySQL binary logs take up disk space. To free up space, purge them from time to time. One
way to do this is by deleting the binary logs that are no longer needed, such as when we make a full
backup:

shell>

mysqldump --single-transaction --flush-logs --master-data=2 \

--all-databases --delete-master-logs > backup_sunday_1_PM.sql

Note

Deleting the MySQL binary logs with

mysqldump --delete-master-logs

can be dangerous if your server is a replication master server, because slave
servers might not yet fully have processed the contents of the binary log. The

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