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