Db schema changed on upgrade without noticeable warning, world of pain to downgrade

[obadz]

While working with @shlevy on #994, I accidentally upgraded my db schema from version 7 to 9.

I looked at the changes which added a couple columns and deleted a table. I tried to revert via sql statements but got tangled in the triggers.

In the end, I was able to get back to a stable state via:

$ nix-store --dump-db > db.txt
$ mv -v /nix/var/nix/db /nix/var/nix/db.old
$ nix-store --load-db < db.txt

(I suspect someone going through the same issues without doing the failed SQL wizardry might have to dump the db using nix-store from the newer version, and reload it using nix-store from the older version)

I would suggest:

1. That there be an appropriate warning and user acknowledgment when the db is irreversibly upgraded
2. That the above procedure be documented somewhere

[basvandijk]

I also just ran into this problem. I was able to resolve it by removing /nix/var/nix/db and running nixops deploy again which recreates the nix db.

[dtzWill]

Just ran into this problem today, and just wanted to thank you for this and share a bit of what was needed to resolve my schema version problems.
In my particular case, I had nixUnstable in my profile and somehow managed to upgrade the system schema to '10' which is too new for my 16.09 system.

Here's what I ended up doing, written up after the fact but in hopes it helps someone in the future:

• Stop nix-daemon
  $ sudo systemctl stop nix-daemon
$ sudo systemctl stop nix-daemon.socket

• Use 'new' Nix from my profile to dump the current DB:
  $ NIX_REMOTE= sudo -E nix-store --dump-db > db.txt
  (EDIT: it might not be necessary to clear NIX_REMOTE; @LnL7 points out the nix-daemon isn't used when invoked by root)

• Move current db to the side:
  $ sudo su
# mv /nix/var/nix/db /nix/var/nix/db.old

• Import the saved DB using the "old" Nix
  # nix-store --load-db < db.txt

• Remove the new Nix from my profile so it won't cause problems again
  # nix-env -p /nix/var/nix/profiles/per-user/will/profile -e nix

• Start the nix-daemon again, all should be well:
  # systemctl start nix-daemon.socket

[LnL7]

The NIX_REMOTE environment variable is only set when the db is not writable for the user. https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/misc/nix-daemon.nix#L406-L408

[stale]

I marked this as stale due to inactivity. → More info

[stale]

I closed this issue due to inactivity. → More info