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Re: [Sketch] Don't checksum reliable transmissions

From: Branko ─îibej <brane_at_xbc.nu>
Date: Tue, 04 May 2010 15:32:32 +0200

On 03.05.2010 23:05, Stefan Fuhrmann wrote:
> Blair Zajac wrote:
>> On 5/2/10 8:56 AM, Philipp Marek wrote:
>>> Hello Stefan!
>>>
>>>> The idea is the following: ra_local (and possibly others)
>>>> are "reliable" in that they won't corrupt transmission.
>>>> For now, this implies that we don't need to checksum
>>>> the data again. There might be more shortcuts that
>>>> can be taken in the future.
>>> ...
>>>> With all other patches applied, this saves 15% runtime
>>>> in 'svn export file://'. However, rev'ing svn_delta_editor_t
>>>> seems only be feasible in context of 'editor v2'.
>>> I understand your point, and 15% sound very interesting.
>>>
>>> But I'd like to note that even for local operations it's a nice
>>> feature to avoid data
>>> corruption via software bugs (off-by-one and similar), and over LAN
>>> it's nice to have,
>>> too (eg. because of bugs in switches and routers, see eg.
>>> http://www.cs.pitt.edu/~kyoungsoo/cs2520/papers/CRC_TCP_Checksum.pdf).
>>>
>>> As the WAN (Internet) uses the same protocols as a LAN (TCP, IP)
>>> following that argument
>>> would mean that the checksum is informational only, and doesn't need
>>> to be checked.
>>>
>>>
>>> So I'd propose that this would be configurable for the paranoid
>>> people (like me, maybe ;-).
>>
>> Given the size of the patch, reving of the API and that I like the
>> checksum to always be done, I would just have svn always perform the
>> checksums.
>>
> But you know that today ra_local does NOT checksum
> for certain operations, at least for single file gets / exports.
> However, I can see the point in making it a client-side option -
> maybe on a per-server basis just like everything else in
> the 'servers' config file.

Doing a checksum on the client-side is sane and expected when you
receive data from the server. It opens a security hole if you stop the
server from checksumming the data it receives in turn.
Received on 2010-05-04 15:33:08 CEST

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