Useful SQL Statements to Check What Makes FND_LOBS Grow? (Doc ID 1245974.1)
How to Find Lengtht of the Attachments Uploaded of Documents of Record? (Doc ID 1580234.1)
How To Determine The Size of a File In Table FND_LOBS? (Doc ID 401094.1)
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Also search MOS for FND_LOBS and/or FND_ATTACHED_DOCUMENTS and you should get many hits.