ps_tokudb_admin should prevent activating TokuBackup if there is no TokuDB engine on server

[Shahriyar Rzayev]

As mentioned in Documentation:
"Percona TokuBackup is an open-source hot backup utility for MySQL servers running the TokuDB storage engine"

https://www.percona.com/doc/percona-server/5.6/tokudb/toku_backup.html

If there is no TokuDB engine in server TokuBackup should not exist as well.
But with ps_tokudb_admin we can install TokuBackup even if there is no TokuDB:

mysql> select plugin_name, plugin_status from information_schema.plugins where plugin_name like '%toku%';
Empty set (0.00 sec)

sh@percona-XPS-15:~$ sudo ps_tokudb_admin --enable-backup -uroot -p12345

mysql> select plugin_name, plugin_status from information_schema.plugins where plugin_name like '%toku%';
+---------------+---------------+
| plugin_name | plugin_status |
+---------------+---------------+
| tokudb_backup | ACTIVE |
+---------------+---------------+
1 row in set (0.00 sec)

Resulting in inconsistent situation -> if try to take a backup:

mysql> set tokudb_backup_dir='/home/tokubackupdir';
ERROR 1193 (HY000): Unknown system variable 'tokudb_data_dir'

[Roel Van de Paar (roel11)]

Updated triage. To avoid confusion from users, and based on discussions re: TB/XB this is a rather important fix to get in.

[Tomislav Plavcic (tplavcic)]

Ok. Here's another one - what if you have both installed and then try to uninstall just TokuDB and leave TokuBackup installed?
I guess it should be handled the same so if you try something like that you should get an error.

[Shahriyar Rzayev (rzayev-sehriyar)]

+Agree:
1. Installing TokuBackup should be prevented if there is no TokuDB engine (this report)
2. Say TokuDB engine and TokuBackup installed, then if somebody removes TokuDB, TokuBackup should be removed as well or invalidated in some way. (will report new)

[Shahriyar Rzayev (rzayev-sehriyar)]

Reported as -> https://bugs.launchpad.net/percona-server/+bug/1520472

[Roel Van de Paar (roel11)]

Great. Looking forward to a fix on both of them. If we make many of these little tweaks, TB will overall become a much more user friendly product.

[Tomislav Plavcic (tplavcic)]

PR: https://github.com/percona/percona-server/pull/250

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-946