On 1/10/2011 4:20 PM, Phil Stracchino wrote:
> On 01/10/11 15:48, Mike Ruskai wrote:
>
>> I know how to backup the database. That's not my question. My question
>> is how to create a schedule, in an environment with multiple concurrent
>> jobs, that guarantees that the catalog backup runs after all other
>> scheduled jobs, and by itself.
>>
>> So if I have three machines currently running a backup job
>> simultaneously, the catalog backup has to wait until they finish, even
>> if the maximum number of concurrent jobs is four. Once they do finish,
>> and the catalog backup starts, no other jobs can start until the catalog
>> backup is complete.
>>
>> Can this be done in Bacula, or do I need to do custom synchronization in
>> run-before scripts?
>>
> If you set the Catalog job to a lesser priority (say, 15, where the
> highest priority is 1, and most normal jobs are priority 10), you
> guarantee that the Catalog job will not be started while any
> higher-priority job is running.
>
> Guaranteeing that no higher-priority job can start while the Catalog job
> is running is a more difficult problem, but one that usually isn't an
> issue unless you typically have jobs running around the clock and being
> started at varying intervals. However, since the DB dump or snapshot
> that typically starts most DB backup schemes should be an atomic
> operation that occurs with the tables locked, if another job starts
> while your catalog job is running it really shouldn't matter. It's not
> going to be able to modify the catalog while the catalog is being dumped.
>
>
I should have read more carefully about concurrent jobs. It seems that
enabling it basically kills your ability to prioritize jobs, since only
jobs of the same priority run at the same time (and the mixed priority
option only minimally changes that). So if there are X concurrent jobs,
and X currently running jobs, it's not possible to queue up another ten
jobs and have them consume the available backup slots in a specific
order based on priority. They will presumably run in the order they are
started, which means the scheduler has to take over as the priority manager.
So simply having the catalog backup be a different priority ensures that
no other job can run at the same time, provided mixed priorities are
disallowed (that would allow the higher-priority backup jobs to start
while the catalog backup is under way). Which is just as well, since I
don't like the idea of relying on database or table locks.
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