Last night we crossed over 16,777,216 comments in the database. The wise amongst you might note that this number is 2^24, or in MySQLese an unsigned mediumint. Unfortunately, like 5 years ago we changed our primary keys in the comment table to unsigned int (32 bits, or 4.1 billion) but neglected to change the index that handles parents. We're awesome! Fixing is a simple ALTER TABLE statement... but on a table that is 16 million rows long, our system will take 3+ hours to do it, during which time there can be no posting. So today, we're disabling threading and will enable it again later tonight. Sorry for the inconvenience. We shall flog ourselves appropriately. Update: 11/10 12:52 GMT by J : It's fixed.