A lowly developer splits his working time between home and the company premises. He uses the following routine: at the end of the working day at home/company, he compresses the source tree and picks it up on his USB stick. At company/home, he decompresses the package and hacks on.
This procedure is starting to show some issues, however. For one, the data barely fit in the USB stick, even compressed. He is contemplating a bigger USB stick (maybe one of the new USB hard drives), but even if he uses that, the problem is that the procedure takes too long: the repository snapshot he works on is huge, and compressing it and taking it with him simply takes too long.
Of course, if this developer had a fast Internet access at home, he could use rsync; that is, provided that the company allows remote access at all - but does it?
And, naturally, the changes he makes daily couldn't possibly be that big - why should he take a whole source tree every time?
He defends himself, saying that he must be absolutely certain that everything is updated, and that he couldn't just take patch files for his work, since other parts of the tree are updated by others. What else could he do?
Well, there is something...
What if we didn't use the network to send the CRCs and the
What if we just stored them, inside, say, a USB stick?
That's exactly the idea that rdiff implements. You can download the source code and compile it for yourself here (as part of librsync), or get it pre-compiled for your platform (under Debian, apt-get install rdiff is enough).
Here is a simple example of its usage, to update a single file:
(At home) /home/jdoe/code$ rdiff signature SrcFileA.c SrcFileA.c.signature (The CRCs of the blocks in file SrcFileA.c are now stored in SrcFileA.c.signature. You take the .signature file to work) (At work) /home/JohnDoe/code$ rdiff delta SrcFileA.c.signature \ SrcFileA.c SrcFileA.c.delta (Using the CRCs calculated at home, find the differences of the work file and store them in SrcFileA.c.delta) (Back home) /home/jdoe/code$ rdiff patch SrcFileA.c SrcFileA.c.delta \ SrcFileA.c.new (update SrcFileA.c to SrcFileA.c.new using the deltas)Right!
The results are depicted in the "screenshot" below:
(At home) /home/jdoe/code$ snapOldData.pl SrcTree/ /home/jdoe/code$ ls -lF drwxr-xr-x 7 jdoe coder 0 Mar 24 13:07 SrcTree/ -rw-r--r-- 12345 jdoe coder 0 Mar 24 13:07 SrcTree.signs.tar.bz2 /home/jdoe/code$ cp SrcTree.signs.tar.bz2 /mnt/usbstick/ (At work) /home/JohnDoe/code$ cp /mnt/usbstick/SrcTree.signs.tar.bz2 . /home/JohnDoe/code$ createDeltas.pl work/ SrcTree.signs.tar.bz2 /home/JohnDoe/code$ ls -lF drwxr-xr-x 7 jdoe coder 0 Mar 24 13:07 work/ -rw-r--r-- 12345 jdoe coder 0 Mar 24 13:07 work.deltas.tar.bz2 -rw-r--r-- 12345 jdoe coder 0 Mar 24 13:07 SrcTree.signs.tar.bz2 /home/JohnDoe/code$ rm /mnt/usbstick/SrcTree.signs.tar.bz2 /home/JohnDoe/code$ cp work.deltas.tar.bz2 /mnt/usbstick/ (Back home) /home/jdoe/code$ cp /mnt/usbstick/work.deltas.tar.bz2 . /home/jdoe/code$ applyDeltas.pl work.deltas.tar.bz2 SrcTree/The scripts will also update the home work tree with all the new files that have appeared, and they will keep a backup of the files changed (with the extension .rdiff_oldVersion) so that you can revert to your old versions if you so wish.
You can download them here:
Some stats from a Pentium D at 2.8 GHz, running a Debian Linux VMWARE image:
The source tree weighs in at 350MB.
(At home) Size of signature file: 3.9MB
(At work) Time it takes to generate deltas: 5min
(At work) Size of generated "deltas" file: 6.5MB
(Back home) Time it takes to apply the deltas: 6min
(Looks like I won't be replacing my 256MB USB stick
any time soon.)
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