TRIM_HORIZON vs LATEST

Question

I can't find in the formal documentation of AWS Kinesis any explicit reference between TRIM_HORIZON and the checkpoint, and also any reference between LATEST and the checkpoint.

Can you confirm my theory:

• TRIM_HORIZON - In case the application-name is new, then I will read all the records available in the stream. Else, application-name was already used, then I will read from my last checkpoint.

• LATEST - In case the application-name is new, then I will read all the records in the stream which added after I subscribed to the stream. Else, application-name was already used, I will read messages from my last checkpoint.

• The difference between TRIM_HORIZON and LATEST is only in case the application-name is new.

Answer 1

From GetShardIterator documentation (which lines up with my experience using Kinesis):

In the request, you can specify the shard iterator type AT_TIMESTAMP to read records from an arbitrary point in time, TRIM_HORIZON to cause ShardIterator to point to the last untrimmed record in the shard in the system (the oldest data record in the shard), or LATEST so that you always read the most recent data in the shard.

Basically, the difference is whether you want to start from the oldest unprocessed record (TRIM_HORIZON), or from "right now" (LATEST - skipping data between latest checkpoint and now).