Monitoring global tables

Important

This documentation is for version 2017.11.29 (Legacy) of global tables, which should be avoided for new global tables. 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.

You can use Amazon CloudWatch to monitor the behavior and performance of a global table. Amazon DynamoDB publishes ReplicationLatency and PendingReplicationCount metrics for each replica in the global table.

• ReplicationLatency—The elapsed time between when an updated item appears in the DynamoDB stream for one replica table, and when that item appears in another replica in the global table. ReplicationLatency is expressed in milliseconds and is emitted for every source- and destination-Region pair.

  During normal operation, ReplicationLatency should be fairly constant. An elevated value for ReplicationLatency could indicate that updates from one replica are not propagating to other replica tables in a timely manner. Over time, this could result in other replica tables falling behind because they no longer receive updates consistently. In this case, you should verify that the read capacity units (RCUs) and write capacity units (WCUs) are identical for each of the replica tables. In addition, when choosing WCU settings, follow the recommendations in Global tables version.

  ReplicationLatency can increase if an AWS Region becomes degraded and you have a replica table in that Region. In this case, you can temporarily redirect your application's read and write activity to a different AWS Region.

• PendingReplicationCount—The number of item updates that are written to one replica table, but that have not yet been written to another replica in the global table. PendingReplicationCount is expressed in number of items and is emitted for every source- and destination-Region pair.

  During normal operation, PendingReplicationCount should be very low. If PendingReplicationCount increases for extended periods, investigate whether your replica tables' provisioned write capacity settings are sufficient for your current workload.

  PendingReplicationCount can increase if an AWS Region becomes degraded and you have a replica table in that Region. In this case, you can temporarily redirect your application's read and write activity to a different AWS Region.

For more information, see DynamoDB Metrics and dimensions.