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Re: [PATCH] Re: BerkeleyDb on NetApp NFS [#14837]

From: Keith Bostic <keith.bostic_at_oracle.com>
Date: 2006-06-28 22:30:49 CEST

On Jun 28, 2006, at 4:00 PM, C. Michael Pilato wrote:

> Keith Bostic wrote:
>> I'd suggest the following wording:
>>
>> If you are using a repository with the Berkeley DB back end (default
>> for repositories created with Subversion 1.0 and 1.1, not the default
>> thereafter), do not access the repository via NFS. Althought Berkeley
>> DB supports database storage on remote file systems, not all
>> Subversion
>> functionality with be available in this configuration.
>
> Hrm. "Not all Subversion functionality will be available" seems a bit
> vague, and still leads folks to believe that there's some
> Subversion-related
> value to be had in putting their BDB-backed repositories on NFS (of
> which I
> can fathom none). I think the key points to make here are:
>
> * you CANNOT safely access an NFS-hosted Subversion repository from
> multiple NFS clients, period.

Agreed. (Well, unless all of the databases are read-only, but you
still need local directories for the shared region files.)

> * you CAN safely access an NFS-hosted Subversion repository from
> a single
> NFS client if, and only if, the NFS implementation is up to
> par. (What
> was the criteria, here -- ability to support file-backed
> shared memory
> regions, or something?)

You can move Berkeley DB databases and log files to a remote
filesystem, as long as sync works, that is, as long as you can flush
to the disk. I don't know of any current NFS implementations where
that's not the case.

You can move Berkeley DB shared region files to a remote filesystem
if the filesystem supports mapping files into process memory (some
do), and supports correct semantics for mutexes in the shared memory
if the mapping succeeds (almost none do).

> * you CAN configure your repository to house its database and
> logfiles
> on NFS, but some Subversion functionality won't work (due to
> shortcomings in Subversion). And of course, since the repository
> itself isn't on NFS, it isn't accessible via any NFS clients.

How about:

If you are using a repository with the Berkeley DB back end (default
for repositories created with Subversion 1.0 and 1.1, not the default
thereafter), we do not recommend storing the repository on a remote
filesystem (for example, NFS). While Berkeley DB databases and log
files can be stored on remote filesystems, the Berkeley DB shared
region files cannot be stored on a remote filesystem, the remote
filesystem is only accessible to a single filesystem client, and not
all Subversion functionality will be available for the repository.

--keith

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Received on Thu Jun 29 21:27:21 2006

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