Best practices and requirements for managing global tables

Using Amazon DynamoDB global tables, you can replicate your table data across AWS Regions. It is important that the replica tables and secondary indexes in your global table have identical write capacity settings to ensure proper replication of data.

Global tables version

There are two versions of DynamoDB global tables available: Global Tables version 2019.11.21 (Current) and Global tables version 2017.11.29 (Legacy). Customers should use Global Tables version 2019.11.21 (Current) when possible, as it provides greater flexibility, higher efficiency and consumes less write capacity than 2017.11.29 (Legacy).

To determine which version you are using, see Determining the DynamoDB global table version you are using. To update existing global tables from Version 2017.11.29 (Legacy) to Version 2019.11.21 (Current), see Upgrading global tables.

Requirements for adding a new replica table

If you want to add a new replica table to a global table, each of the following conditions must be true:

If global secondary indexes are specified, the following conditions must also be met:

Best practices and requirements for managing capacity

Consider the following when managing capacity settings for replica tables in DynamoDB.

Using DynamoDB auto scaling

Using DynamoDB auto scaling is the recommended way to manage throughput capacity settings for replica tables that use the provisioned mode. DynamoDB auto scaling automatically adjusts read capacity units (RCUs) and write capacity units (WCUs) for each replica table based upon your actual application workload. For more information, see Managing throughput capacity automatically with DynamoDB auto scaling.

If you create your replica tables using the AWS Management Console, auto scaling is enabled by default for each replica table, with default auto scaling settings for managing read capacity units and write capacity units.

Changes to auto scaling settings for a replica table or secondary index made through the DynamoDB console or using the UpdateGlobalTableSettings call are applied to all of the replica tables and matching secondary indexes in the global table automatically. These changes overwrite any existing auto scaling settings. This ensures that provisioned write capacity settings are consistent across the replica tables and secondary indexes in your global table. If you use the UpdateTable, RegisterScalableTarget, or PutScalingPolicy calls, you should apply the change to each replica table and matching secondary index individually.

Managing capacity manually

If you decide not to use DynamoDB auto scaling, you must manually set the read capacity and write capacity settings on each replica table and secondary index.

The provisioned replicated write capacity units (rWCUs) on every replica table should be set to the total number of rWCUs needed for application writes across all Regions multiplied by two. This accommodates application writes that occur in the local Region and replicated application writes coming from other Regions. For example, suppose that you expect 5 writes per second to your replica table in Ohio and 5 writes per second to your replica table in N. Virginia. In this case, you should provision 20 rWCUs to each replica table (5 + 5 = 10; 10 x 2 = 20).

To update write capacity settings for your global table, we strongly recommend using the DynamoDB console or the UpdateGlobalTableSettings API operation. UpdateGlobalTableSettings applies changes to write capacity settings to all replica tables and matching secondary indexes in a global table automatically. If you use the UpdateTable, RegisterScalableTarget, or PutScalingPolicy operations, you should apply the change to each replica table and matching secondary index individually. For more information, see Amazon DynamoDB API Reference.