Following, you can find specific information about working with read replicas on RDS for MySQL. For general information about read replicas and instructions for using them, see Working with read replicas. Before a MySQL DB instance can serve as a replication source, make sure to enable automatic backups on the source DB instance. To do this, set the backup retention period to a value other than 0. This requirement also applies to a read replica that is the source DB instance for another read replica. Automatic backups are supported for read replicas running any version of MySQL. You can configure replication based on binary log coordinates for a MySQL DB instance. On RDS for MySQL version 5.7.23 and higher MySQL 5.7 versions and RDS for MySQL 8.0.26 and higher 8.0 versions, you can configure replication using global transaction identifiers (GTIDs). For more information, see Using GTID-based replication for Amazon RDS for MySQL. You can create up to 15 read replicas from one DB instance within the same Region. For replication to operate effectively, each read replica should have the same amount of compute and storage resources as the source DB instance. If you scale the source DB instance, also scale the read replicas. RDS for MySQL supports cascading read replicas. To learn how to configure cascading read replicas, see . You can run multiple read replica create and delete actions at the same time that reference the same source DB instance. When you perform these actions, stay within the limit of 15 read replicas for each source instance. A read replica of a MySQL DB instance can't use a lower DB engine version than its source DB instance. If your MySQL DB instance uses a nontransactional engine such as MyISAM, you need to perform the following steps to successfully set up your read replica. These steps are required to make sure that the read replica has a consistent copy of your data. These steps are not required if all of your tables use a transactional engine such as InnoDB.
You can use replication filters to specify which databases and tables are replicated with a read replica. Replication filters can include databases and tables in replication or exclude them from replication. The following are some use cases for replication filters:
You can also use replication filters to specify which databases and tables are replicated with a primary MySQL DB instance that is configured as a replica in an inbound replication topology. For more information about this configuration, see Configuring binary log file position replication with an external source instance. To configure replication filters, set the following replication filtering parameters on the read replica:
The parameters are evaluated in the order that they are listed. For more information about how these parameters work, see the MySQL documentation: By default, each of these parameters has an empty value. On each read replica, you can use these parameters to set, change, and delete replication filters. When you set one of these parameters, separate each filter from others with a comma. You can use the The binary logging format of the source DB instance is important for replication because it determines the record of data changes. The setting of the All data definition language (DDL) statements are replicated as statements, regardless of the The following limitations apply to replication filtering for RDS for MySQL:
To configure replication filtering for a read replica, modify the replication filtering parameters in the parameter group associated with the read replica. You can't modify a default parameter group. If the read replica is using a default parameter group, create a new parameter group and associate it with the read replica. For more information on DB parameter groups, see Working with parameter groups. You can set parameters in a parameter group using the AWS Management Console, AWS CLI, or RDS API. For information about setting parameters, see . When you set parameters in a parameter group, all of the DB instances associated with the parameter group use the parameter settings. If you set the replication filtering parameters in a parameter group, make sure that the parameter group is associated only with read replicas. Leave the replication filtering parameters empty for source DB instances. The following examples set the parameters using the AWS CLI. These examples set The following examples set replication filters: Example Including databases in replication The following example includes the For Linux, macOS, or Unix: For Windows: Example Including tables in replication The following example includes the For Linux, macOS, or Unix: For Windows: Example Including tables in replication using wildcard characters The following example includes tables with names that begin with For Linux, macOS, or Unix: For Windows: Example Escaping wildcard characters in names The following example shows you how to use the escape character Assume that you have several table names in database For Linux, macOS, or Unix: For Windows: Example Excluding databases from replication The following example excludes the For Linux, macOS, or Unix: For Windows: Example Excluding tables from replication The following example excludes tables For Linux, macOS, or Unix: For Windows: Example Excluding tables from replication using wildcard characters The following example excludes tables with names that begin with For Linux, macOS, or Unix: For Windows: You can view the replication filters for a read replica in the following ways:
You can use delayed replication as a strategy for disaster recovery. With delayed replication, you specify the minimum amount of time, in seconds, to delay replication from the source to the read replica. In the event of a disaster, such as a table deleted unintentionally, you complete the following steps to recover from the disaster quickly:
To configure delayed replication for any future read replica created from a DB instance, run the mysql.rds_set_configuration stored procedure with the To configure delayed replication during read replica creation
To modify delayed replication for an existing read replica, run the mysql.rds_set_source_delay stored procedure. To modify delayed replication for an existing read replica
After stopping replication to the read replica, you can start replication and then stop it at a specified binary log file location using the mysql.rds_start_replication_until stored procedure. To start replication to a read replica and stop replication at a specific location
Replication stops automatically when the stop point is reached. The following RDS event is generated: After replication is stopped, in a disaster recovery scenario, you can promote a read replica to be the new source DB instance. For information about promoting a read replica, see . Read replicas are designed to support read queries, but you might need occasional updates. For example, you might need to add an index to optimize the specific types of queries accessing the replica. You can enable updates by setting the You can create a read replica from either single-AZ or Multi-AZ DB instance deployments. You use Multi-AZ deployments to improve the durability and availability of critical data, but you can't use the Multi-AZ secondary to serve read-only queries. Instead, you can create read replicas from high-traffic Multi-AZ DB instances to offload read-only queries. If the source instance of a Multi-AZ deployment fails over to the secondary, any associated read replicas automatically switch to use the secondary (now primary) as their replication source. For more information, see Multi-AZ deployments for high availability. You can create a read replica as a Multi-AZ DB instance. Amazon RDS creates a standby of your replica in another Availability Zone for failover support for the replica. Creating your read replica as a Multi-AZ DB instance is independent of whether the source database is a Multi-AZ DB instance. RDS for MySQL supports cascading read replicas. With cascading read replicas, you can scale reads without adding overhead to your source RDS for MySQL DB instance. With cascading read replicas, your RDS for MySQL DB instance sends data to the first read replica in the chain. That read replica then sends data to the second replica in the chain, and so on. The end result is that all read replicas in the chain have the changes from the RDS for MySQL DB instance, but without the overhead solely on the source DB instance. You can create a series of up to three read replicas in a chain from a source RDS for MySQL DB instance. For example, suppose that you have an RDS for MySQL DB instance,
You can't create another read replica beyond this third cascading read replica in the series for For cascading read replicas to work, each source RDS for MySQL DB instance must have automated backups turned on. To turn on automatic backups on a read replica, first create the read replica, and then modify the read replica to turn on automatic backups. For more information, see . As with any read replica, you can promote a read replica that's part of a cascade. Promoting a read replica from within a chain of read replicas removes that replica from the chain. For example, suppose that you want to move some of the workload from your
For more information about promoting read replicas, see . For MySQL read replicas, you can monitor replication lag in Amazon CloudWatch by viewing the Amazon RDS Previous versions of MySQL used Common causes for replication lag for MySQL are the following:
When the You can stop and restart the replication process on an Amazon RDS DB instance by calling the system stored procedures mysql.rds_stop_replication and mysql.rds_start_replication. You can do this when replicating between two Amazon RDS instances for long-running operations such as creating large indexes. You also need to stop and start replication when importing or exporting databases. For more information, see Importing data to an Amazon RDS MariaDB or MySQL database with reduced downtime and Exporting data from a MySQL DB instance by using replication. If replication is stopped for more than 30 consecutive days, either manually or due to a replication error, Amazon RDS terminates replication between the source DB instance and all read replicas. It does so to prevent increased storage requirements on the source DB instance and long failover times. The read replica DB instance is still available. However, replication can't be resumed because the binary logs required by the read replica are deleted from the source DB instance after replication is terminated. You can create a new read replica for the source DB instance to reestablish replication. Troubleshooting a MySQL read replica problemFor MySQL DB instances, in some cases read replicas present replication errors or data inconsistencies (or both) between the read replica and its source DB instance. This problem occurs when some binary log (binlog) events or InnoDB redo logs aren't flushed during a failure of the read replica or the source DB instance. In these cases, manually delete and recreate the read replicas. You can reduce the chance of this happening by setting the following parameter values: In the parameter group associated with the source DB instance, we recommend keeping these parameters values: Failure to follow this guidance increases the risk of read replicas presenting replication errors or data inconsistencies (or both) between the read replica and its source DB instance. The replication technologies for MySQL are asynchronous. Because they are asynchronous, occasional You can do several things to reduce the lag between updates to a source DB instance and the subsequent updates to the read replica, such as the following:
Amazon RDS monitors the replication status of your read replicas and updates the You can review the details of the associated error thrown by the MySQL engine by viewing the One common issue that can cause replication errors is when the value for the Other common situations that can cause replication errors include the following:
If you decide that you can safely skip an error, you can follow the steps described in the section . Otherwise, you can first delete the read replica. Then you create an instance using the same DB instance identifier so that the endpoint remains the same as that of your old read replica. If a replication error is fixed, the |
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