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Hello, developers. |
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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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PORTAGE_COMPRESS=xz |
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in make.globals. |
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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 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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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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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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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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Depending on the expected amount of complexity, I'd either go for: |
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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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2) -Ne with minimal 'N' for CompCPU==8 and DictSize > filesize -- still |
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max compression ratio while keeping lowest memory requirements possible. |
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Your thoughts? |
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-- |
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Best regards, |
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Michał Górny |
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