Also, an approach from a big company like youtube, have you noticed that their viewed history disappears after a while? For example, you watched a video one year ago, and now it doesn’t have that “Watched” mark. That’s because they are keeping a limited number of Watched videos. When you watch a new video and exceed the limit of 200 Watched videos, they are deleting one Watched video (the oldest one). You can do the same trick not to make an oversized DB.
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