Posted: 15/Jan/2024
Need to implement atomic counter using DynamoDB? If you have a use-case that can tolerate over-counting or under-counting (for example, visitor count), use the UpdateItem API.
Here is an example that uses the SET operator in an update expression to increment num_logins attribute:
resp,err:=client.UpdateItem(context.Background(),&dynamodb.UpdateItemInput{TableName:aws.String(tableName),Key:map[string]types.AttributeValue{"email":&types.AttributeValueMemberS{Value:email},},UpdateExpression:aws.String("SET num_logins = num_logins + :num"),ExpressionAttributeValues:map[string]types.AttributeValue{":num":&types.AttributeValueMemberN{Value:num,},},ReturnConsumedCapacity:types.ReturnConsumedCapacityTotal,})Note that every invocation of UpdateItem will increment (or decrement) - hence it is not idempotent.
Recommended reading - Atomic Counters
