subversion and psd files - why are revisions so large?

Question

I've started using svn with Versions.app locally, as I want to keep trace of each significat change of my photoshop files. I was sick of saving the same file every hour naming it ..._v1, v2,v45 etc, I thought it would take less space to use svn but I guess I was wrong. I've noticed that revisions saved in svn repository are really large, much larger that the original file. Is there a way to reduce it, or is this normal behaviour? Then I'm asking myself what's the point of such solution... If this is easier than I'm thinking, excuse me my poor knowledge, I've never used svn before.

Answer 1

Subversion and other version control systems try to reduce the amount of storage they use by determining the differences between two versions of a file and storing that instead of both whole files. This works well for text, since line endings are a natural start/end of blocks of characters that are likely to change. Files whose line endings are fluid and automatically generated or do not have line endings at all are likely to produce a worst-case result from the difference detector, resulting in a file that basically contains both original files.

PSDs are not line based, so it is normal for them to take a lot of space in version control. In addition they use compression, so a single change will cause the layer data to be completely different after the point of change with nothing in common with the original even at a binary level.

If you're willing to live with larger PSD files there may be a way to turn off the compression and allow a binary difference to be smaller. See the directions on Adobe's site.