Thank you for your quick answer. Yes, I have checked the site and I do not see any relevance to me. I only use python script to create the dictionary. SELECT is within SQlite shell. I have checked lsof - nothing beside sqlite3 is accessing the file The timestamp on the file does not change. I understand that SELECT should not write to the database but somehow the file get corrupted after several searches without timestamp changed. When I copy the backup it starts again fine and it is getting worse and worse since my search are having more and more "disk image is malformed" problems. This makes the database practically unusable. The problem does not appear on the database ~10x smaller (~20GB) but maybe I have not performed enough searches since larger the database the fewer searches are needed to create this problem. Best regards, Witek