I was in the process of upgrading my installation from 1.15.0 to 1.16.0 this morning and I made a backup copy of the database using phpMyAdmin. I suspect that's not recommended and I can see why the instructions use mysqldump instead. Believe me, I'll do it the "right" way from now on. In any case, after upgrading the PHP and running update.php, the site wasn't working. I figured I'd restore the database and start over.
It turns out phpMyAdmin didn't do a very good job of exporting my database. I did manage to recreate my database from an older backup and then went through the phpMyAdmin dump table by table, since most of them seemed fine.
There were, it turns out, two problems, one more serious than the other.
First, in the categorylinks table, it didn't put single quotes around the dates for some reason. I was able to add them easily enough (regex replace is a godsend!).
The other problem was in the objectcache. For some reason, the contents of that are mostly giberish. The 'value' field in that table is a mediumblob but there are other tables with mediumblobs that didn't cause any problems. Is the content of that table different in some way that causes this problem?
Actually, while I'm interested in the above my real question is how serious is it that this table is now out of sync with the rest of the database? Obviously I've lost something but is it serious?