Re:Saving Data: Reducing the Size of App Updates by 65%
by adrianN on Wednesday December 07, 2016 @06:37AM
(#13121847)
I looked in the 7z manual but couldn't find anything obviously related to this functionality. Would you mind giving a reference?
Re:Saving Data: Reducing the Size of App Updates by 65%
by user5994461 on Wednesday December 07, 2016 @10:19AM
(#13123107)
'gzip --rsyncable' for gzip.
I couldn't find the equivalent for 7z in a quick glance. It supports at least 5 compression algorithms so there is probably not a general option. Maybe one has to play with the advanced settings per algorithm, if they support it.
Re:Saving Data: Reducing the Size of App Updates by 65%
by JoshTriplett on Wednesday December 07, 2016 @10:54AM
(#13123428)
gzip --rsyncable does make gzip set boundaries so one change doesn't affect the entire rest of the file, just one block.
However, the resulting differences don't seem nearly as amenable to the bsdiff algorithm as the changes to the underlying uncompressed data. In almost all cases, you'll likely get better results with bsdiff on the uncompressed data (and bsdiff internally compresses its result).
Re:Saving Data: Reducing the Size of App Updates by 65%
by user5994461 on Wednesday December 07, 2016 @05:07PM
(#13126703)
Don't know about how bsdiff operate, maybe it's naive.
Good deduplication and diff algorithms have adaptive block size detection.
The flag will modify the storage format, -kinda packing files/chunk together instead of just compressing into a huge block- so that tools can detect diff and same sections over the full archive.
It's not well know but it is an absolute must known. e.g. for backup archive that goes over rsync, and change little over time.