Why does the classic resize of my Amazon Redshift cluster take so long to complete?

Resolution

The time required for your Amazon Redshift cluster to complete a classic resize might vary from several hours to several days. The classic resize of your cluster can take longer for the following reasons:

• Read workload on the source cluster
• Number and size of the tables being transferred
• Table definition and skewed tables
• The number and types of nodes that are used in the source and target clusters

Reduce the downtime for a classic resize

To reduce the time that's required for a classic resize, complete the following tasks:

• Use the Amazon Redshift console to monitor the status of your resize operation. On the Cluster details page, choose the Status tab to view the average rate of transfer, elapsed time, and remaining time.
• Fix skewed tables, and choose an appropriate distribution key. For more information, see Amazon Redshift engineering's advanced table design playbook: distribution styles and distribution keys.
• Remove unused tables. To identify unused tables, run the unscanned_table_summary.sql script from the GitHub website.
  Note: The unscanned table summary shows only the history from the past few days. To capture usage data over a longer period of time, use the SystemTablePersistence utility from the GitHub website.
• Use elastic resize to add or remove nodes on an existing Amazon Redshift cluster and automatically redistribute data to the new nodes. Because elastic resize doesn't create a new cluster, the downtime is significantly lower than the downtime for a classic resize. For more information, see Resizing clusters in Amazon Redshift.

For more information about how to optimize your resize performance, see Top 10 performance tuning techniques for Amazon Redshift.

Troubleshoot classic resize

To troubleshoot classic resize issues, complete the following tasks:

• If your cluster has a status of NONE in the AWS Command Line Interface (AWS CLI), then the target cluster is still being provisioned. Wait until your target cluster is provisioned. After the cluster is copied over, the status changes to IN_PROGRESS.
  Note: If you receive errors when you run AWS CLI commands, then see Troubleshoot AWS CLI errors. Also, make sure that you're using the most recent AWS CLI version.
• If you receive an error message about insufficient disk space, then your data doesn't fit into the target cluster. Resize your Amazon Redshift cluster with more nodes, a different distribution style, or a different node type. For more information, see Resizing clusters in Amazon Redshift.
• To cancel a resize operation before it completes, choose Cancel resize from the Cluster details page in the Amazon Redshift console. Or, run the cancel-resize command from the AWS CLI.
  Note: You can't cancel the resize operation when it's in the final stage.

Related information

How do I resize an Amazon Redshift cluster?

Why does a table in an Amazon Redshift cluster consume more or less disk storage space than expected?