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Amazon DynamoDB
Developer Guide (API Version 2012-08-10)

Read Consistency

Amazon DynamoDB is available in multiple AWS regions around the world. Each region is independent and isolated from other AWS regions. For example, if you have a table called People in the us-east-2 region and another table named People in the us-west-2 region, these are considered two entirely separate tables. For a list of all the AWS regions in which DynamoDB is available, see AWS Regions and Endpoints in the Amazon Web Services General Reference.

Every AWS region consists of multiple distinct locations called Availability Zones. Each Availability Zone is isolated from failures in other Availability Zones, and to provide inexpensive, low-latency network connectivity to other Availability Zones in the same region. This allows rapid replication of your data among multiple Availability Zones in a region.

When your application writes data to a DynamoDB table and receives an HTTP 200 response (OK), all copies of the data are updated. The data is eventually consistent across all storage locations, usually within one second or less.

DynamoDB supports eventually consistent and strongly consistent reads.

Eventually Consistent Reads

When you read data from a DynamoDB table, the response might not reflect the results of a recently completed write operation. The response might include some stale data. If you repeat your read request after a short time, the response should return the latest data.

Strongly Consistent Reads

When you request a strongly consistent read, DynamoDB returns a response with the most up-to-date data, reflecting the updates from all prior write operations that were successful. A strongly consistent read might not be available if there is a network delay or outage.

Note

DynamoDB uses eventually consistent reads, unless you specify otherwise. Read operations (such as GetItem, Query, and Scan) provide a ConsistentRead parameter. If you set this parameter to true, DynamoDB uses strongly consistent reads during the operation.