Versioned Data Sources
AWS AppSync currently supports versioning on DynamoDB data sources. Conflict Detection, Conflict Resolution, and Sync operations require a Versioned data source. When you enable versioning on a data source, AWS AppSync will automatically:
Enhance items with object versioning metadata.
Record changes made to items with AWS AppSync mutations to a Delta table.
Maintain deleted items in the Base table with a “tombstone” for a configurable amount of time.
Versioned Data Source Configuration
When you enable versioning on a DynamoDB data source, you specify the following fields:
BaseTableTTL
The number of minutes to retain deleted items in the Base table with a “tombstone” - a metadata field indicating that the item has been deleted. You can set this value to 0 if you want items to be removed immediately when they are deleted. This field is required.
DeltaSyncTableName
The name of the table where changes made to items with AWS AppSync mutations are stored. This field is required.
DeltaSyncTableTTL
The number of minutes to retain items in the Delta table. This field is required.
Delta Sync Table
AWS AppSync currently supports Delta Sync Logging for mutations using PutItem, UpdateItem, and DeleteItem DynamoDB operations.
When an AWS AppSync mutation changes an item in a versioned data source, a record of that change will be stored in a Delta table that is optimized for incremental updates. You can choose to use different Delta tables (e.g. one per type, one per domain area) for other versioned data sources or a single Delta table for your API. AWS AppSync recommends against using a single Delta table for multiple APIs to avoid the collision of primary keys.
The schema required for this table is as follows:
ds_pk
A string value that is used as the partition key. It is constructed by concatenating the Base data source name and the ISO8601 format of the date the change occurred. (e.g. Comments:2019-01-01)
ds_sk
A string value that is used as the sort key. It is constructed by concatenating the IS08601 format of the time the change occurred, the primary key of the item, and the version of the item. The combination of these fields guarantees uniqueness for every entry in the Delta table (e.g. for a time of 09:30:00 and an ID of 1a and version of 2, this would be 09:30:00:1a:2)
_ttl
A numeric value that stores the timestamp, in epoch seconds, when an item should be removed from the Delta table. This value is determined by adding the DeltaSyncTableTTL value configured on the data source to the moment when the change occurred. This field should be configured as the DynamoDB TTL Attribute.
The IAM role configured for use with the Base table must also contain permission to operate on the Delta table. In this example, the permissions policy for a Base table called Comments and a Delta table called ChangeLog is displayed:
