Dnia 2014-01-17, o godz. 19:19:14 Duncan <1i5t5.dun...@cox.net> napisał(a):
> Michał Górny posted on Fri, 17 Jan 2014 17:27:30 +0100 as excerpted: > > > Now some numbers. I did some tests 'converting' late gx86 daily tarballs > > to squashfs. I've used squashfs 4.2 with LZO compression since it's > > quite good and very fast. > > > > 96M portage-20140108.sqfs > [...] > > 97M portage-20140114.sqfs > > 97M portage-20140115.sqfs > > > > For deltas [...] > > > > 4,9M portage-20140108.sqfs-portage-20140109.sqfs.vcdiff.djw > > 6,3M portage-20140109.sqfs-portage-20140110.sqfs.vcdiff.djw > [...] > > 8,5M portage-20140114.sqfs-portage-20140115.sqfs.vcdiff.djw > > > > As you can see, the deltas are quite large compared to the actual > > changes. However, we could have expected that since we're diffing a > > compressed filesystem. What's important, however, is that applying it > > takes ~2.5 second on my 2 GHz Athlon64. > > And... eyeballing a 6 MiB average, diffs are ~1/16 the full squashfs > size, perhaps a bit larger. So people updating once a week or even about > every 10 days would see a bandwidth savings, provided the sync script was > intelligent enough to apply updates serially. > > The breakover point would be roughly an update every two weeks, or twice > a month, at which point just downloading a new full squashfs would be > easier, at about the same bandwidth. Yes, that's the initial goal. The update code would catch that condition and perform full fetch instead. However, it may be actually beneficial to provide other durations, like weekly deltas. In my tests, the daily updates for this week summed up to almost 50M while the weekly was barely 20M. > > What do you think? > > How does this, particularly the metadata cache, interact with overlays? > That's /my/ big question. The same way as usual. Nothing special happens unless you override eclasses via overlays. If you do that, you need unionfs to save the cache updates -- but then, it has no point for you to use squashfs. -- Best regards, Michał Górny
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