@scott, @devstorm,
Thank you for all your suggestion for the solution.
I understand that MySQL max_allowed_packet limit is changeable,
so I will try setting it as high as possible.
If not possible, then I might have to set the file mode as an alternative.
Scanning checksum data should be another good idea, but to do that, I have to revise the program so that checksum data can be inserted in DB table, and that will take a lot of time if I assign it to every website I own.
(But if the future wpfmp will have that feature, then I want to try it!)