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.
