Dirty Upgrade

Users of TokuDB expect to be able to take a live snapshot of the TokuDB data and log files and use them with newer versions of the software. Since the snapshot of the TokuDB's recovery log may occur when TokuDB is running, the recovery log does not have a shutdown log entry at the end of the log. Unfortunately, TokuDB will not run if its recovery log was not cleanly shut down and the version of the recovery log is older than the current version of TokuDB. This interferes with upgrades.

See MDEV-6173 and MDEV-6165 for details.

We are going to allow upgrades of dirty TokuDB logs from versions >= 7.1.5 to TokuDB 7.5. This is easy since there have been no changes to the recovery and rollback logs from versions 25 except for the version number. All of the version changes are in the fractal tree layouts, and the fractal tree code knows how to parse multiple layouts.

We are not going to allow upgrades of dirty TokuDB logs from versions < 7.1.5 because the cost to implement the code to handle old recovery log entries is too high.