CODEWITHSUNDEEP
amazon-dynamodb
Alexander Patrikalakis
Alexander Patrikalakis

Reputation: 5205

How do I keep track of the most recent time an item was read in DynamoDB?

I have a use case where I want to always know and be able to look up DynamoDB items by their last read time. What is the easiest way to do this (I would prefer not to use any other services).

Upvotes: 1

Views: 685

Answers (1)

Alexander Patrikalakis
Alexander Patrikalakis

Reputation: 5205

You can recall items by their last read time in DynamoDB by using a combination of the UpdateItem API, Query API and GSIs.

  1. Estimate the amount of time your application will randomly read 1MB worth of items from the DynamoDB table. Let's assume that we are working with small items and that each item is <=1KB, so then, if the RPS on the table is 100, it will take 10 seconds for your application to randomly read 1MB of data.

  2. Create a GSI that projects all attributes and is keyed on (PK=read_time_bucket, SK=read_time). The WPS on the GSI should equal the RPS of the base table in the case of small items.

  3. Use the UpdateItem API with the following parameters to “read” each item. The UpdateItemResult will contain the item and the updated last read time and bucket.:

    (
    ReturnAttributes=ALL_NEW, 
    UpdateExpression="SET read_time_bucket = :bucket, read_time = :time", 
    ExpressionAttributeValues={
        ":bucket": <a partial timestamp indicating the 10-second-long bucket of time that corresponds to now>, 
        ":time": <epoch millis>
    }
)

  4. You can use the Query API to look up items by last read time on the GSI, using key conditions on read_time_bucket and read_time. You will need to adjust your time bucket size and throughput settings depending on item size and read/write patterns on the base table. If item size is prohibitively large, restrict the projection to SELECTED_ATTRIBUTES or KEYS_ONLY.

Upvotes: 1

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