title: DynamoDB Triggers (Streams + Lambda) : details on TRIM_HORIZON?
body: <p>I want to process recent updates on a DynamoDB table and save them in another one. Let's say I get updates from an IoT device irregularly put in Table1, and I need to use the N last updates to compute an update in Table2 for the same device in sync with the original updates (kind of a sliding window).</p>
  
  <p>DynamoDB Triggers (Streams + Lambda) seem quite appropriate for my needs, but I did not find a clear definition of <code>TRIM_HORIZON</code>. In some docs I understand that it is the oldest data in Table1 (can get huge), but in other docs it would seems that it is 24h. Or maybe the oldest in the stream, which is 24h?</p>
  
  <p>So anyone knows the truth about <code>TRIM_HORIZON</code>? Would it even be possible to configure it? </p>
  
  <p>The alternative I see is not to use <code>TRIM_HORIZON</code>, but rather tu use <code>LATEST</code> and perform a query on Table1. But it sort of defeats the purpose of streams.</p>