[Python-bugs-list] [ python-Bugs-584409 ] add way to detect bsddb version

[noreply@sourceforge.net]

Bugs item #584409, was opened at 2002-07-21 00:29
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=584409&group_id=5470

Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: paul rubin (phr)
Assigned to: Nobody/Anonymous (nobody)
Summary: add way to detect bsddb version

Initial Comment:
The bsddb module docs say that some Python
configurations use Berkeley db 1.85
and others use the incompatible 2.0.  Maybe by now
there are later versions as well.  There's no way
listed for a Python script to know which version of
bsddb is running underneath!  That's not so great,
since the versions don't interoperate and don't support
the same operations.

Proposed fix: please add a new function to the module,
bsddb.db_version().  This would
return a constant string like "1.85" or "2.0", built at
Python configuration time.


----------------------------------------------------------------------

Comment By: Nobody/Anonymous (nobody)
Date: 2002-07-23 16:35

Message:
Logged In: NO 

How can it be "impossible" to find out?  The build script
for the bsddb module can check what version is being linked,
and include a string reachable from Python.

At worst, there could be a routine added to the module that
actually creates a database, then examines the db file and
figures out from the bytes inside which version it is.

Paul


----------------------------------------------------------------------

Comment By: Martin v. Löwis (loewis)
Date: 2002-07-23 14:50

Message:
Logged In: YES 
user_id=21627

I also believe that this problem should be fixed by importing 
pybsddb3.

On this issue itself: it turns out impossible to find out, 
programmatically, what version of Sleepycat DB you are 
running if all you have is the compatibility API: both the 
compile-time and the run-time version information is not 
available. Furthermore, you cannot include both new and old 
headers, since they conflict. So given the current code base, 
this problem cannot be solved.

----------------------------------------------------------------------

Comment By: Skip Montanaro (montanaro)
Date: 2002-07-22 18:18

Message:
Logged In: YES 
user_id=44345

Sorry for the lack of clarity.  What I should have said is that the code 
which implements the bsddb extension module only calls the 
1.85-compatible C API exposed when you configure the Berkeley DB 
code using the --enable-compat185 flag.  All the wonders and mysteries 
of the later parts of the API are lost on the bsddb code.

There are two levels of compatibility, the API level and the file format 
level.  All users of the bsddb module should care about is the file format 
level compatibility and handling that is a one-time problem dealt with 
using tools provided by Sleepycat as part of their distribution.

The topic of including bsddb3 in the standard distribution has been 
discussed before.  For one example, see:

  http://mail.python.org/pipermail/python-dev/2002-January/019261.html

I think the main stumbling block to incorporation is that it only works 
with versions 3 and 4 of the Berkeley DB library.  There is a more recent 
thread that currently escapes my feeble attempts to find it.



----------------------------------------------------------------------

Comment By: paul rubin (phr)
Date: 2002-07-22 13:26

Message:
Logged In: YES 
user_id=72053

OK, it looks like both the docs and Skip's note are a bit
unclear.  When you say only the 1.85 API is exposed, does
that mean the 1.85 file format is also used either way?  In
particular, if Python is linked with Berkeley DB 2.0 and I
create a db with it, will that db interoperate with another
application that's linked to Berkeley DB 1.85?

If it won't interoperate, then it's definitely worthwhile to
add some kind of call to the Python bsddb module to let
Python scripts find out which file format they're dealing
with.  

Also, I didn't realize only the 1.85 API was supported.  I
hope pybsddb3 can become part of the standard Python
distribution, since I'd like to use Sleepycat's transaction
features from Python scripts.

----------------------------------------------------------------------

Comment By: Skip Montanaro (montanaro)
Date: 2002-07-22 05:31

Message:
Logged In: YES 
user_id=44345

This is an interesting idea, but one that I think is less useful than you 
might believe.  The bsddb module exposes the same API based on the 
1.85 C API regardless what version of Berkeley DB you link with.  (I 
have linked it with versions 1.85 through 4.something.)  I've been using 
the bsddb module since its inclusion in Python and have never actually 
cared what version of the underlying C API the module what linked with. 
Someone programming to the C API *would* care about version 
differences, because the C API has grown richer over the years.  The 
bsddb module code just hasn't ever used any new functionality.  Note 
that the pybsddb3 module does use the new functionality in the version 
3 and 4 APIs.

What changes on you between versions are the file formats, and you 
should only care about that at the point where you upgrade from one 
version of Berkeley DB to another.  (Generally, you realize this when you 
start getting errors trying to open old databases.)  Sleepycat provides 
command line tools to help you convert from one file version to another, 
so once you realize your file formats have changed, you wind up poking 
around your disk looking for old format Berkeley DB files, run the tools 
on them, then go back to more interesting things, like writing 
stable sorts. ;-)


----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=584409&group_id=5470