What are the prospects of recovering old version of file on BTRFS

There is a useful post on LinuxQuestions by rayfordj that suggest that it may be possible to restore a vg/lv, even after a sequence of lvremove && vgremove && pvremove.

The sequence on the posting is:

1. pvcreate --restorefile /etc/lvm/archive/ --uuid dev/sdX
2. vgcfgrestore -f /etc/lvm/archive/ --verbose thisVG
3. vgdisplay -v /dev/thisVG && vgchange -ay /dev/thisVG
4. mount /dev/thisVG/missingLV /mnt

(Please check these steps for your situation carefully before using, or use the text from the original posting which is much clearer!).

Step number 4. will probably fail and will require a file system check.

Following your description of the problem you may be able to jump to step 2.

There is also an article on LinuxJournal about recovering data from a failed RAID array and LVM vg here.

Considering these two sources, it seems to me that you should be able to diff the current lvm config file and the archived one, and try using the old one instead of the new one. If you are lucky restarting lvm will magically allow you to see the lv with lvdisplay, and then mount it.

You reinstalled the operating system and are surprised that it over-wrote the database files? Methinks you're a bit out of your depth here.

While there's a very small chance that some of the database files could be recovered, it's going to take some work, most likely by a professional data recovery outfit ala Kroll Ontrack.

Honestly your best bet is to restore from backup and be done with it. That's going to be your quickest path back to a functional system