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From Stefan Fuhrmann <stefan.fuhrm...@wandisco.com>
Subject Re: new svnfsfs tool
Date Mon, 19 May 2014 06:56:57 GMT
On Sat, May 17, 2014 at 10:10 AM, Branko ─îibej <brane@wandisco.com> wrote:

>  On 16.05.2014 19:56, Stefan Sperling wrote:
>
> On Thu, May 15, 2014 at 10:48:37AM -0000, stefan2@apache.org wrote:
>
>  Author: stefan2
> Date: Thu May 15 10:48:37 2014
> New Revision: 1594860
>
> URL: http://svn.apache.org/r1594860
> Log:
> Introduce FSFS expert tool 'svnfsfs'.  It is intended to grow various
> FSFS-specific commands in the future - like recreating repcache.db etc.
>
> For now, it provides two commands to read (dump) and write (load)
> format 7 index information.  With these, corrupted repositories can
> be manipulated / fixed by hand or script.
>
> The former fsfs-stats tool becomes a sub-command as well.
>
>  Wouldn't it make sense to integrate such functionality in svnadmin?
>
>
> If the tool is strictly for fiddling with internals of FSFS repositories
> that cannot meaningfully apply to other backends, then no, probably not ...
> we really don't want to have backend-specific commands in svnadmin.
>

I agree.

But I also see Stefan's implicit point of having fewer tools
and doing things consistently over e.g. all backends. My
rationale is as follows: Is there a reasonable way to define
FS vtable functions that will provide the necessary data in
a mostly generic way?

For the "recreate rep-cache.db" mentioned in the log message,
it would certainly be possible to add an '--rebuild-caches' option.
This is fairly generic and should therefore go into svnadmin,
unless we needed some more specific option or UI interaction.

OTOH, it would be very hard to define a generic read/write
interface for backend-specific index data. So, dump-index
and load-index are better of in a separate tool that directly
calls into the FSFS lib.

The 'stats' sub-command is a borderline case. Lots of the
grouping etc. may work for FSX as well. However, the container-
based structure of FSX may require a different data structure
(1 additional level of indirection?) and it is too early to design
what the interface should look like. So, for now it's fine to have
it in the extra tool (at least dropping fsfs-stats in the process)
but later the code may be moved behind the FS API.

As for svn-bench, yes it would be conceivable to add a '--null'
option to the standard client UI. But there are a few issues
with that approach. First, we may not support all other options
of the respective command when in '--null' mode. That's not
terribly bad but there would be more to test or we may get
the occasional bug report.

Secondly, svn-bench is intended to be a minimalistic protocol
driver. It takes various shortcuts and even duplicates and
modifies code from the client lib (and possibly others) to
bypass client-side bottlenecks.

So again, having one tool instead of two would be nice but
the overall coding, testing and maintenance effort may then
bit higher than with the current setup.

-- Stefan^2.

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