MySQL 9.1 Release Notes
If the source database contains existing data it is necessary to copy this data to each replica. There are different ways to dump the data from the source database. The following sections describe possible options.
To select the appropriate method of dumping the database, choose between these options:
Use the mysqldump tool to create a dump of all the databases you want to replicate. This is the recommended method, especially when using
InnoDB.If your database is stored in binary portable files, you can copy the raw data files to a replica. This can be more efficient than using mysqldump and importing the file on each replica, because it skips the overhead of updating indexes as the
INSERTstatements are replayed. With storage engines such asInnoDBthis is not recommended.Use MySQL Server's clone plugin to transfer all the data from an existing replica to a clone. For instructions to use this method, see Section 7.6.7.7, “Cloning for Replication”.
Tip
To deploy multiple instances of MySQL, you can use InnoDB Cluster which enables you to easily administer a group of MySQL server instances in MySQL Shell. InnoDB Cluster wraps MySQL Group Replication in a programmatic environment that enables you easily deploy a cluster of MySQL instances to achieve high availability. In addition, InnoDB Cluster interfaces seamlessly with MySQL Router, which enables your applications to connect to the cluster without writing your own failover process. For similar use cases that do not require high availability, however, you can use InnoDB ReplicaSet. Installation instructions for MySQL Shell can be found here.
To create a snapshot of the data in an existing source database, use the mysqldump tool. Once the data dump has been completed, import this data into the replica before starting the replication process.
The following example dumps all databases to a file named
dbdump.db, and includes the
--source-data option which
automatically appends the CHANGE
REPLICATION SOURCE TO statement required on the
replica to start the replication process:
$> mysqldump --all-databases --source-data > dbdump.db
Note
If you do not use
--source-data, then it is
necessary to lock all tables in a separate session manually.
See Section 19.1.2.4, “Obtaining the Replication Source Binary Log Coordinates”.
It is possible to exclude certain databases from the dump
using the mysqldump tool. If you want to
choose which databases to include in the dump, do not use
--all-databases. Choose one
of these options:
Exclude all the tables in the database using
--ignore-tableoption.Name only those databases which you want dumped using the
--databasesoption.
Note
By default, if GTIDs are in use on the source
(gtid_mode=ON),
mysqldump includes the GTIDs from the
gtid_executed set on the
source in the dump output to add them to the
gtid_purged set on the
replica. If you are dumping only specific databases or
tables, it is important to note that the value that is
included by mysqldump includes the GTIDs
of all transactions in the
gtid_executed set on the
source, even those that changed suppressed parts of the
database, or other databases on the server that were not
included in the partial dump. Check the description for
mysqldump's --set-gtid-purged option to
find the outcome of the default behavior for the MySQL
Server versions you are using, and how to change the
behavior if this outcome is not suitable for your situation.
For more information, see Section 6.5.4, “mysqldump — A Database Backup Program”.
To import the data, either copy the dump file to the replica, or access the file from the source when connecting remotely to the replica.
This section describes how to create a data snapshot using the raw files which make up the database. Employing this method with a table using a storage engine that has complex caching or logging algorithms requires extra steps to produce a perfect “point in time” snapshot: the initial copy command could leave out cache information and logging updates, even if you have acquired a global read lock. How the storage engine responds to this depends on its crash recovery abilities.
If you use InnoDB tables, you can
use the mysqlbackup command from the MySQL Enterprise Backup
component to produce a consistent snapshot. This command
records the log name and offset corresponding to the snapshot
to be used on the replica. MySQL Enterprise Backup is a commercial product that
is included as part of a MySQL Enterprise subscription. See
Section 32.1, “MySQL Enterprise Backup Overview” for detailed
information.
This method also does not work reliably if the source and
replica have different values for
ft_stopword_file,
ft_min_word_len, or
ft_max_word_len and you are
copying tables having full-text indexes.
Assuming the above exceptions do not apply to your database,
use the cold backup
technique to obtain a reliable binary snapshot of
InnoDB tables: do a
slow shutdown of the
MySQL Server, then copy the data files manually.
To create a raw data snapshot of
MyISAM tables when your MySQL
data files exist on a single file system, you can use standard
file copy tools such as cp or
copy, a remote copy tool such as
scp or rsync, an
archiving tool such as zip or
tar, or a file system snapshot tool such as
dump. If you are replicating only certain
databases, copy only those files that relate to those tables.
For InnoDB, all tables in all databases are
stored in the system
tablespace files, unless you have the
innodb_file_per_table option
enabled.
The following files are not required for replication:
Files relating to the
mysqldatabase.The replica's connection metadata repository file
master.info, if used; the use of this file is now deprecated (see Section 19.2.4, “Relay Log and Replication Metadata Repositories”).The source's binary log files, with the exception of the binary log index file if you are going to use this to locate the source binary log coordinates for the replica.
Any relay log files.
Depending on whether you are using InnoDB
tables or not, choose one of the following:
If you are using InnoDB tables,
and also to get the most consistent results with a raw data
snapshot, shut down the source server during the process, as
follows:
Acquire a read lock and get the source's status. See Section 19.1.2.4, “Obtaining the Replication Source Binary Log Coordinates”.
In a separate session, shut down the source server:
$> mysqladmin shutdownMake a copy of the MySQL data files. The following examples show common ways to do this. You need to choose only one of them:
$> tar cf /tmp/db.tar ./data $> zip -r /tmp/db.zip ./data $> rsync --recursive ./data /tmp/dbdataRestart the source server.
If you are not using InnoDB
tables, you can get a snapshot of the system from a source
without shutting down the server as described in the following
steps:
Acquire a read lock and get the source's status. See Section 19.1.2.4, “Obtaining the Replication Source Binary Log Coordinates”.
Make a copy of the MySQL data files. The following examples show common ways to do this. You need to choose only one of them:
$> tar cf /tmp/db.tar ./data $> zip -r /tmp/db.zip ./data $> rsync --recursive ./data /tmp/dbdataIn the client where you acquired the read lock, release the lock:
mysql> UNLOCK TABLES;
Once you have created the archive or copy of the database, copy the files to each replica before starting the replication process.