Hi @Matthew ,
To begin with, maybe this article will solve some of your questions: https://nation.marketo.com/t5/Knowledgebase/Marketo-Activities-Data-Retention-Policy/ta-p/251480.
Depending on the information in particular, it's stored from 90 days (high volume activities like emails sent, visits to web pages etc.), to 25 months (low volume activities like email bounces or being added to an opportunity).
Information about people who unsubscribed from your emails is kept separately and for longer, not sure exactly how long.
This is called "durable unsubscribe", you can read a bit on it here: https://docs.marketo.com/display/public/DOCS/Durable+Unsubscribe
I agree with @SanfordWhiteman/. To better answer your question we would need more detail around what you mean with "uploading" and "clearing".
With "uploading" do you refer to import a list of records / persons to the database?
These stay on your database until you contract with Marketo ends or you delete them. Now, there is a difference between emptying a list (=clearing) and deleting records (=delete person).
Below is a screenshot of a static list view where I selected three records. Notice how I highlighted "delete person" in red and "remove from list" in yellow. Keep in mind that deleting cannot be reverted, while clearing can be reverted.
When you delete records, if any of them unsubscribed, they will be deleted from Marketo (and optionally, your main CRM if you choose to), but a record of their email address and the fact they unsubscribed will still be kept somewhere in Marketo's servers.
This is to prevent that people who unsubscribed, and get deleted for whatever reason, are emailed again by mistake if they enter your system again (i.e. they change their mind and resusbcribe or a sales rep adds them manually again).
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