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Always have year, month, day in filename to easily sort it out.
If file is uploaded by user, add user_id in filename, or some
other unique identifier depends on your business in which you require to
upload.
Personally, I always add timestamp and extra data in filename to avoid duplicate.
Example filename:
yyyy/mm/dd/{user_id}-{timestamp}-{extra}.ext
Be careful with /, too much nested folder is no good for
backup (as they say, idk if true or not, but less folder mean less
complicated to me).
Add time postfix to make sense.
Instead of create_at, use create_at_ms.