Dynamodb infrequently scheduled scan

Question

I am implementing a session table with nodejs which will grow to a huge number of items. each hash key is a uuid representing a user.

In order to delete the expired sessions, I must scan the table for expired attribute and delete old sessions. I am planning to do this scan once a few days, and other than that, I don't really need high read capacity.

I came out with 2 solutions, and i would like to hear some feedback about them.

1) UpdateTable to higher capacities for only that scheduled routine, and after the scan is done, simply reduce the table capacities to it's original values.

2) Perform the scan, and when retrieving the 'LastEvaluatedKey' after an x*MB read, create a initiation delay (for not consuming all read/sec units), and then continue the scan with 'ExclusiveStartKey'.

Answer 1

If you're doing a scan, option 1 is your best best. This is the only real way to guarantee that you won't effect your application performance while the scan is ongoing.

The only thing you need to be sure of is that you only run this operation once a day -- I believe you can only DOWNGRADE throughput units on a DynamoDB table 2x's per day (at most).

Answer 2

This is an old question, but I saw it through a related question.

There is now a much better native solution: DynamoDB Time to Live

It allows you to specify one attribute per table that serves as the time to live value for each item. You can then set the attribute per item with a Unix-Timestamp that specifies when the item should be deleted.

Within about 24 hours of that timestamp, the item will be deleted at no additional charge.