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Re: [Bacula-devel] libdbi backend to catalog database


On Saturday 02 February 2008 00.03:13 David Boyes wrote:
> > Kern> When the Bacula drivers become shared objects, Bacula will be
> > Kern> capable of working with multiple different database types
> > Kern> simultaneously so any new implementation should include that
> > Kern> possibility.
>
> I wish you luck in supporting it -- you're going to need it.
>
> I think the problems of using multiple databases for Bacula internals
> and supporting multiple types of database clients are substantially
> different, and if you want to support multiple types of databases for
> the internals you'll either need to federate the disparate databases
> into one view, or pick one for Bacula's internal use and stick with it.
> I think there are serious integrity problems that you'll need to solve
> if you want to use federated databases for Bacula internals (eg,
> holographic table storage, and you'll need to deal with some really hard
> failure scenarios that Just Aren't Worth It).

Well, Bacula already supports multiple types of databases.  It has a single 
view of such databases, and *very* little code varies from database to 
database (unfortunately SQL is not standardized like C).  What Bacula 
currently supports is multiple databases but of a single type per Bacula 
binary.  In the future, it will evolve to multiple databases but of multiple 
types that are supported.  The details support for the SQL servers is not in 
Bacula's domain but rather what the SQL provider must support, so I don't see 
any additional support requirements here other than to ensure that it is 
clear in the job reports what database engine is being used ...

>
> Reading a simple sequential file on daemon startup and storing the value
> in a global variable for use by the various database routines passes the
> KISS test in my book, but YMMV. Putting it a current config file is OK
> too. In either case, get the value at startup, stuff it somewhere and
> pass it behind the scenes.

OK, for me it is much easier to put it in the current conf file.  It is one 
define in a header table, one entry in a look up table and one entry to 
release the allocated memory -- rather trivial. Reading a new file requires 
lots of extra stuff ...

>
> > So why is this a good thing?  I've never understood the idea to have
> > different catalogs either, or what the design goal is.
>
> The original purpose of using the libdbi interface is to remove the
> details of the database implementation from the core Bacula code, which
> allows support of a much wider range of database engines without
> recoding for each one. Libdbi supports postgres, mysql, DB/2, Oracle,
> Sybase, kdb, etc, etc via vendor-supplied (and supported) plugins.
>
> As far as different catalogs go, I've never seen a point in it. Others
> may vary.

They are very useful for improving performance and for scaling while keeping a 
single point of control (Director).


>
> > Should I be using different catalogs for each client?
>
> Not unless you have lots of free time to reconcile them in case of a
> disaster.
>
> > Should I be
> > using different Pools for each client?
>
> You can, but I wouldn't recommend it unless you have very odd retention
> or audit requirements for different clients AND lots of spare time to
> debug things.

Good advice.

Kern

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