Impact on Performance When Saving History

[joebot]

I think the ability to save the History of your work is a really amazing feature in Affinity Photo. As a newbie that was pretty excited about this feature, I have been turning it on for all of my work. However, after noticing some slow-downs and crashes, I have been trying to figure out how much of an impact history has on performance and file size. I'm curious how much space it takes up in a file. More importantly, I am curious what sort of impact saving history has on performance. I am running Affinity on a fairly old Macbook Pro, so any tweaks I can make to get things running more efficiently will help.

 

So, I guess I am asking two things:

 

1: Does saving the history with your file have a big impact on performance while working?

 

2: How much does the history affect file size?

[Ben]

1) Performance while working should not be affected.  When a save happens, there will be some work being done to save any new pixel data.  Because of how we structure our documents, only portions that have been added or altered are saved.

 

The auto-backup feature will cause a save at intervals, but this can be halted if you are in the middle of drawing, so again should not affect using tools.  If you perform a full save there will be time taken to save any new pixel data, and you will have to wait until the save has completed (with a progress bar).  The more drawing you have done, the more pixel data will need to be saved.

 

With a full save, we also do periodic clean-up of your file (to remove wasted space).  This may take additional time at the end of your save, which will be longer if your document history is longer and contains lots of pixel drawing changes.

 

2) The file size will obviously be much larger - you are going to be saving the incremental changes to the state of the document on top of the data required for the document itself.  Again, we only save the small changes at each increment, so it will be as efficient as possible, but saving history does mean that there is a considerable overhead in file size.  To test this you can always save a copy of your file without history and compare the two file sizes.

 

The increase in size will depend largely on how you work.  If you over-draw pixel data a lot, the history will have to save more pixel data in addition to the pixel data required for the document.  If you just add more new pixel data (new layers), then the history will just reference the pixel data used in the document, so the overhead will be less.