Amazon DynamoDB Provisioned Throughput (iOS SDK)

4
votes

I am new to DynamoDB. I am very much confused about provisioned throughput. I am creating a iPhone game in which the users can chat within the game. I am having a Chat table. The Chat table contains GameID, UserID and Message. How do I find the size of the item to calculate throughput. The size of the item entirely depends on the Message right? How to calculate the size of an item?

Amazon tells that we can either modify the throughput by using UpdateTable API or by manually from the console. If I want to change it form code, how will I know that the provisioned throughput has been exceeded for a certain table? How to check that from code?

I am also confused about the CloudWatch. How to understand this?

Could anyone please help me? Please don't point me to the documentation.

Thanks.

1
iosamazon-web-servicesamazon-dynamodbamazon-cloudwatch
Do you really want a database for having users chat to each other? That doesn't really seem like the right way to model it. If you really want to use AWS to support this (questionable on it's own), then maybe something like SQS would work better? - xaxxon
I want the chat to be stored so that they may see their chats in the future. So I am using DynamoDB. - EmptyStack
Not sure that's really the right technology, though. aws.amazon.com/dynamodb/faqs/#DynamoDB_storage_cost_seems_high DynamoDB is for high-throughput, latency sensitive applications. THat seems to likely be the opposite of what you have. - xaxxon
Good point. I agree. Thanks. Now consider my application is not a chat application. Now answer my question. - EmptyStack
Question still really doesn't make sense. DDB isn't made for a bunch of unrelated processes to put stuff into. THe place you know your rate has exceeded is when you try to add/read stuff, it tells you. The answer is your clients will know, but obviously you can't give them the credentials to set your scaling. Have your clients push messages into SQS and then have a master process pull those in and push them into DDB if you must. That process will know if your rate is exceeded and could bump the limit.. but I still think you're using the wrong tool. - xaxxon

1 Answers

4
votes

I will do my best to help with the confusion.

  • DynamoDB is a key:value database
  • CloudWatch is Amazon's products monitoring tool
  • Provisioned throughput is roughly the number Items KB you plan to Read/Write per seconds

Whenever you exceed your provisioned throughput,

  1. DynamoDB answers with ProvisionedThroughputExceededException
  2. DynamoDB notifies CloudWatch

What Cloudwatch does is basically record and aggregates data-points. For most applications, it will only keep track of aggregated data over each consecutive 5min periods.

You can then access these data for "manual" monitoring or set up "alarms". There was a really interesting question on SO a couple of weeks earlier on DynamoDB auto-scaling using alarms. You might be interested in reading it: http://docs.amazonwebservices.com/amazondynamodb/latest/developerguide/ErrorHandling.html

Knowing this, you can start building your application.

As for every DynamoDB services, one needs credentials to access it. Even though they can be restricted to a specific table or set of action, it is very dangerous to bundle them in an application. Would you give MySQL or MongoDB or credentials, even Read Only to any untrusted people ?

May I suggest you do build your application to rely on a server of your own ? This server being trusted and build by you, you could safely perform any authorization check there and grant it full access to your table.

I hope this helps. Feel free to ask for more precisions.