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В Sun, 11 May 2014 19:46:50 +0200 |
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Michał Górny <mgorny@g.o> пишет: |
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|
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> Hello, developers. |
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> |
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> I'd like to raise the following item for discussion: making .xz |
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> the default compressor used by portage for documentation, man pages |
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> and info files. That is, the equivalent of: |
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> |
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> PORTAGE_COMPRESS=xz |
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> |
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> in make.globals. |
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> |
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> Rationale: xz-utils is quite widespread nowadays and it is a part |
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> of @system set. It can achieve better compression ratio than bzip2, |
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> and faster decompression at the same time. |
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|
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I tried it recently. Actually for doc/man/info and any other relatively |
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small text files xz has worse compression ratio than bzip2. See also: |
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|
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https://bugs.gentoo.org/show_bug.cgi?id=372653 |
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|
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> |
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> I have confirmed that both sys-apps/man and sys-apps/man-db can |
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> handle .xz compressed man pages, and sys-apps/texinfo can handle .xz |
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> compressed info pages. Major text editors and pagers support .xz |
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> alike .bz2 (i.e. usually they support both or neither :)). |
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> |
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> The additional question is: what preset to use? To help discussing |
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> this, I'd like to quote the tables from 'man xz': |
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> |
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> Preset DictSize CompCPU CompMem DecMem |
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> -0 256 KiB 0 3 MiB 1 MiB |
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> -1 1 MiB 1 9 MiB 2 MiB |
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> -2 2 MiB 2 17 MiB 3 MiB |
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> -3 4 MiB 3 32 MiB 5 MiB |
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> -4 4 MiB 4 48 MiB 5 MiB |
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> -5 8 MiB 5 94 MiB 9 MiB |
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> -6 8 MiB 6 94 MiB 9 MiB |
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> -7 16 MiB 6 186 MiB 17 MiB |
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> -8 32 MiB 6 370 MiB 33 MiB |
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> -9 64 MiB 6 674 MiB 65 MiB |
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> |
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> Preset DictSize CompCPU CompMem DecMem |
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> -0e 256 KiB 8 4 MiB 1 MiB |
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> -1e 1 MiB 8 13 MiB 2 MiB |
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> -2e 2 MiB 8 25 MiB 3 MiB |
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> -3e 4 MiB 7 48 MiB 5 MiB |
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> -4e 4 MiB 8 48 MiB 5 MiB |
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> -5e 8 MiB 7 94 MiB 9 MiB |
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> -6e 8 MiB 8 94 MiB 9 MiB |
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> -7e 16 MiB 8 186 MiB 17 MiB |
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> -8e 32 MiB 8 370 MiB 33 MiB |
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> -9e 64 MiB 8 674 MiB 65 MiB |
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> |
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> I'd like to note here that increasing dictionary size over file size |
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> does not improve compression. However, the options involved in CompCPU |
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> may. |
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> |
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> Depending on the expected amount of complexity, I'd either go for: |
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> |
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> 1) -6e (or -6, the default) -- max CompCPU, reasonable use of memory, |
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> and dictionary larger than most (or all?) documents that are going to |
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> be compressed, |
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> |
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> 2) -Ne with minimal 'N' for CompCPU==8 and DictSize > filesize -- |
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> still max compression ratio while keeping lowest memory requirements |
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> possible. |
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> |
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> Your thoughts? |
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> |
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|
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-- |
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Alexander Tsoy |
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