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Re: Debian: apu-config and BDB

On Thursday 22 November 2012, Ben Reser wrote:
> Since the change that was made in reaction to this bug report:
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=622081
> apu-config on Debian has avoided returning the BDB library from
> --libs.  The bug suggests that BDB is related to the DBM support in
> APR Util.  This is actually not the case.  They are two separate
> database interfaces supported by APR Util as can be seen by the two
> separate API pages for them:
> http://apr.apache.org/docs/apr-util/1.4/group___a_p_r___util___d_b_
> d.html vs
> http://apr.apache.org/docs/apr-util/1.4/group___a_p_r___util___d_b_
> m.html

You are confusing two things here. Apr-util dbm is an abstraction for 
key-value-type database libraries of which BDB is one possible 

Apr-util dbd (note the different order of the letters than bdb) is an 
abstraction for sql database engines (e.g. mysql, postgresql, ...).

> The bug also says that it thinks this dependency is useless. It may
> be useless for some projects that aren't using the bdb features of
> the library. Those that are using the bdb features will have
> problems with their build system as a result of this change.
> For example.  Subversion would not detect BDB on Debian based
> systems due to this change (until I made a change to our build
> system to work around this).

Apr-util provides a full abstraction for the dbm backends. There is no 
need and no way for a consumer of the apr-util dbm API to directly 
call functions of the backend library and make them interact with apr-
util's dbm functions. Therefore, on Linux it is unnecessary for any 
consumer of the apr-util dbm API to directly link to the dbm libraries 
(except for linking statically). It is enough that apr-util links to 
the dbm libraries (like DBD). Therefore it is generally a good idea on 
Linux to not output the dbm libraries by default. So, it's more a 
platform specific thing than something related to a specific project.

Subversion is (or was?) using apr-util's detection code of BDB without 
using apr-util's dbm API. This is an abuse of apu-config. There is no 
reason at all why subversion would need to use the same version of BDB 
as apr-util does. In fact, this interdependency had caused problems in 
Debian in the past.

> Ultimately there are two failures here.
> 1) You shouldn't be changing apu-config's output in order to remove
> dependencies that are useless for a particular project.  Rather you
> should patch that's project's use of apu-config to filter those
> things out.
> 2) Passing --dbm-libs to get BDB libraries is wrong.
> I'd strongly advise that this change be reverted and that the
> packages that end up with BDB dependencies that are undesirable be
> fixed. Alternatively, you could add --avoid-bdb and --bdb-libs
> flags to apu-config.  I'd suspect that something like that would
> be accepted upstream by APR-UTIL.

No, it is not. BDB is one dbm provider.

> I'd urge the Debian project not to unilaterally take it upon itself
> to change the default behavior of a configuration tool like this.

We will make changes to make packages work together flawlessly. I 
don't think this particular change is a very intrusive one. But if the 
current subversion still has a problem with it, it may be a good idea 
to make it pass --dbm-libs by default.

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