In this chapter, you will find information to solve some of the more common tasks with MySQL. This includes making backups, running more than one MySQL server daemon on a single machine, and replicating a database using the update or binary logs.
Now that master-slave internal replication is available starting in Version 3.23.15, using the update log to implement replications is not recommended. See section 11 Replication in MySQL.
However, it is still possible to replicate a database by using the
update log or the binary log. See section 23.3 The Update Log. This requires one
database that acts as a master (to which data changes are made) and one
or more other databases that act as slaves. To update a slave, just run
mysql < update_log.* or
mysqlbinlog binary_log.* | mysql.
Supply host, user, and password options that are appropriate for the
slave database, and use the update log from the master database as
If you never delete anything from a table, you can use a
column to find out which rows have been inserted or changed in the table
since the last replication (by comparing the time when you did the
replication last time) and only copy these rows to the mirror.
It is possible to make a two-way updating system using both the update log (for deletes) and timestamps (on both sides). But in that case you must be able to handle conflicts when the same data have been changed in both ends. You probably want to keep the old version to help with deciding what has been updated.
Because replication in this case is done with SQL statements, you should not use the following functions in statements that update the database; they may not return the same value as in the original database:
All time functions are safe to use, as the timestamp is sent to the
mirror if needed.
LAST_INSERT_ID() is also safe to use.
Because MySQL tables are stored as files, it is easy to do a
backup. To get a consistent backup, do a
LOCK TABLES on the
relevant tables followed by
FLUSH TABLES for the tables.
See section 7.32
LOCK TABLES/UNLOCK TABLES Syntax.
See section 7.26
You only need a read lock; this allows other threads to continue to
query the tables while you are making a copy of the files in the
database directory. The
FLUSH TABLE is needed to ensure that
the all active index pages is written to disk before you start the backup.
If you want to make a SQL level backup of a table, you can use
SELECT INTO OUTFILE or
TABLE. See section 7.19
SELECT Syntax. See section 7.13
BACKUP TABLE Syntax.
Another way to back up a database is to use the
mysqldump program or
mysqlhotcopy script. See section 15.7 Dumping the Structure and Data from MySQL Databases and Tables.
See section 15.8 Copying MySQL Databases and Tables.
shell> mysqldump --tab=/path/to/some/dir --opt --full or shell> mysqlhotcopy database /path/to/some/dirYou can also simply copy all table files (`*.frm', `*.MYD', and `*.MYI' files) as long as the server isn't updating anything. The script
mysqlhotcopydoes use this method.
mysqldif it's running, then start it with the
--log-update[=file_name]option. See section 23.3 The Update Log. The update log file(s) provide you with the information you need to replicate changes to the database that are made subsequent to the point at which you executed
If you have to restore something, try to recover your tables using
REPAIR TABLE or
myisamchk -r first. That should work in
99.9% of all cases. If
myisamchk fails, try the following
procedure: (This will only work if you have started MySQL with
--log-update. See section 23.3 The Update Log.):
shell> mysqlbinlog hostname-bin.[0-9]* | mysqlIf you are using the update log you can use:
shell> ls -1 -t -r hostname.[0-9]* | xargs cat | mysql
ls is used to get all the update log files in the right order.
You can also do selective backups with
SELECT * INTO OUTFILE 'file_name'
FROM tbl_name and restore with
LOAD DATA INFILE 'file_name' REPLACE
... To avoid duplicate records, you need a
PRIMARY KEY or a
UNIQUE key in the table. The
REPLACE keyword causes old records
to be replaced with new ones when a new record duplicates an old record on
a unique key value.
If you get performance problems in making backups on your system, you can solve this by setting up replication and do the backups on the slave instead of on the master. See section 11.1 Introduction.
If you are using a Veritas file system, you can do:
FLUSH TABLES WITH READ LOCK
mount vxfs snapshot.
There are circumstances when you might want to run multiple servers on the same machine. For example, you might want to test a new MySQL release while leaving your existing production setup undisturbed. Or you might be an Internet service provider that wants to provide independent MySQL installations for different customers.
If you want to run multiple servers, the easiest way is to compile the servers with different TCP/IP ports and socket files so they are not both listening to the same TCP/IP port or socket file. See section 15.4 mysqld_multi, program for managing multiple MySQL servers.
Assume an existing server is configured for the default port number and
socket file. Then configure the new server with a
something like this:
shell> ./configure --with-tcp-port=port_number \ --with-unix-socket-path=file_name \ --prefix=/usr/local/mysql-3.22.9
file_name should be different than the
default port number and socket file pathname, and the
should specify an installation directory different than the one under which
the existing MySQL installation is located.
You can check the socket used by any currently executing MySQL server with this command:
shell> mysqladmin -h hostname --port=port_number variables
Note that if you specify ``
localhost'' as a hostname,
will default to using Unix sockets instead of TCP/IP.
If you have a MySQL server running on the port you used, you will get a list of some of the most important configurable variables in MySQL, including the socket name.
You don't have to recompile a new MySQL server just to start with
a different port and socket. You can change the port and socket to be used
by specifying them at run time as options to
shell> /path/to/safe_mysqld --socket=file_name --port=port_number
mysqld_multi can also take
as an argument and pass the options from a configuration file to
safe_mysqld and further to
If you run the new server on the same database directory as another
server with logging enabled, you should also specify the name of the log
--log-slow-queries. Otherwise, both servers may be trying to
write to the same log file.
WARNING: Normally you should never have two servers that update data in the same database! If your OS doesn't support fault-free system locking, this may lead to unpleasant surprises!
If you want to use another database directory for the second server, you
can use the
--datadir=path option to
NOTE also that starting several MySQL servers
mysqlds) in different machines and letting them access one data
NFS is generally a BAD IDEA! The problem
is that the
NFS will become the bottleneck with the speed. It is
not meant for such use. And last but not least, you would still have to
come up with a solution how to make sure that two or more
are not interfering with each other. At the moment there is no platform
that would 100% reliable do the file locking (
usually) in every situation. Yet there would be one more possible risk
NFS; it would make the work even more complicated for
lockd daemon to handle. So make it easy for your self and forget
about the idea. The working solution is to have one computer with an
operating system that efficiently handles threads and have several CPUs
When you want to connect to a MySQL server that is running with a different port than the port that is compiled into your client, you can use one of the following methods:
--host 'hostname' --port=port_numberto connect with TCP/IP, or
[--host localhost] --socket=file_nameto connect via a Unix socket.
DBD::mysqlmodule you can read the options from the MySQL option files. See section 4.16.5 Option Files.
$dsn = "DBI:mysql:test;mysql_read_default_group=client;mysql_read_default_file=/usr/local/mysql/data/my.cnf" $dbh = DBI->connect($dsn, $user, $password);
MYSQL_TCP_PORTenvironment variables to point to the Unix socket and TCP/IP port before you start your clients. If you normally use a specific socket or port, you should place commands to set these environment variables in your `.login' file. See section A Environment Variables. See section 15.1 Overview of the Different MySQL Programs.
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