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From David Chapman <dcchap...@acm.org>
Subject Re: Debian Linux 32 vs. 64 bit
Date Mon, 25 Jan 2016 20:33:44 GMT
On 1/25/2016 10:45 AM, Philip Martin wrote:
> David Chapman <dcchapman@acm.org> writes:
>
>> On 1/25/2016 3:59 AM, Niemann, Hartmut wrote:
>>> I want to upgrade my Linux box from Debian Jessie (32bit) to Debian
>>> Jessie (64bit).
>>>
>>> For the transition time, the machine will boot alternating the 32bit
>>> and the 64bit OS.
>>>
>>> I have several SVN repositories and working copies on it.
>>>
>>> Is it safe to share SVN repositories and working copies between
>>> 32bit and 64 bit?
>>>
>>> (Jessie ships with 1.8.10, as far as I know.)
> It should just work for both repositories and working copies.

Is that documented somewhere, such that system administrators can rely 
on it?  Or could a Subversion developer decide to put endian- or 
size-dependent binary data into a repository or working copy file somewhere?

>> I wouldn't try this approach for a machine with repositories.  I had a
>> repository on a 64-bit Linux machine, then bought a 32-bit micro
>> server that I could keep running all the time.  I was unable to copy
>> the repository directory tree directly, even though both were Intel
>> architecture machines.  I had to dump and load (with svnadmin).  I'd
>> be surprised if this has changed in the last three years.
> It's hard to work out what went wrong from that vague description.  In
> the unlikely event that you were using a BDB repository then there are
> BDB library compatibility issues: a recover/upgrade may be needed and
> downgrading to older BDB is not always possible.
>

My notes are vague, unfortunately.  This was back in 2007, when I was 
compiling from tarballs:

1) configure/compile with BDB support on both platforms
2) copy repository directory to 32-bit machine
3) problem found -> dump/load to avoid system dependencies
4) problem solved
5) hey, my repositories are actually FSFS!

I was trying to take good notes, as is my practice for system 
administration tasks that I do once every three years, but somewhere in 
the migration process I failed to write something down.  Item 5) was 
recorded some weeks after the migration, so I don't know when the build 
switched to FSFS support only, relative to the repository directory 
move.  Nor do my notes record what actually got me to a 
production-worthy repository.  So yes, kind of vague.  But enough to get 
me spooked.

I also know from experience that it is very easy to let platform 
dependencies leak into outside data files.  Avoidance takes a concerted 
effort and detection is extremely difficult when testing a build on a 
single machine (here, by definition we're talking about running a single 
repository on two separate machines).  Thus my question about a 
documented promise from Subversion developers.

-- 
     David Chapman      dcchapman@acm.org
     Chapman Consulting -- San Jose, CA
     Software Development Done Right.
     www.chapman-consulting-sj.com


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