Re: bzr commit into mysql-6.0-backup branch (cbell:2712) Bug#33364

[Chuck Bell]

Rafal,

...

> 1. Please explain what is your idea of how the PURGE statements will 
> behave if there is an ongoing BACKUP/RESTORE operation and vice versa 
> (how BACKUP/RESTORE should behave if there is ongoing PURGE operation).

This has been tested. If a backup is running and a PURGE BACKUP LOGS 
command is issued at the same time, the normal locks on the logs will 
apply. The logs are designed to handle this situation. Indeed, a test I 
have been able to reproduce where I stop a backup after it has initiated 
the log handle and then issue a PURGE BACKUP LOGS; shows that upon 
completion of the backup, the backup history table has 1 row (the 
correct one), and the backup_progress has the corresponding progress rows.

However, it is possible to construct a scenario where the PURGE occurs 
near the end of the backup (or restore) and thereby (if a PURGE BACKUP 
LOGS; has been issued) it is possible that there will be no rows in the 
backup_progress log and under the right circumstance no rows in the 
backup_history log. But such is the power of the PURGE BACKUP LOGS command.

Note: I am talking about the least restrictive form of the command 
designed to remove all log entries.

If you feel strongly this is not desired, then we can add a new 
requirement that the purge may not run at the same time as a backup or 
restore, but I really don't see the need for such a limitation.

Chuck