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Am 02.04.2014 14:27, schrieb Douglas J Hunley: |
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> I was reviewing my Portage settings yesterday and I noticed that I have |
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> PORTAGE_COMPRESS set (to bzip2, the default) on both of my servers and |
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> it occurred to me that both of these servers have filesystems that |
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> support compression (btrfs on one, zfs on the other). So I'm wondering |
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> if it still makes sense to have PORTAGE_COMPRESS set or if I should |
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> unset it and just let the fs-level compression handle it. Portage is |
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> already slow, why have it take the time to do this when the fs does it |
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> better and transparently? Thoughts on the matter? |
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I think you have a good point disabling portage compression, but I |
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wanted to correct one statement: Decompression in the kernel takes as |
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much time as decompression in userspace - if it's the same algorithm. |
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The differences here are: |
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* creation of an additional process (bz[ip2, cat]), negligible compared |
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to the cpu time compression takes |
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* bz[ip2, cat] runs in user space (safer) vs in kernel space ("risky") |
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* different [de]compression algorithm (fs usually uses weaker but faster |
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compression algorithms like lz4, lzo or gz) |
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* different [de]compression setting (portage uses -9, kernel at best -6 |
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- the difference in the resulting file size is small, but the difference |
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in used cpu time is high) |
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For me two things decide the question: |
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* Assuming you write more man pages than you read, and disk space is not |
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an issue, a weaker compression ratio to save cpu time makes sense. |
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* If you have compression _already_ on for the fs, then compressing |
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textual data before storing it on that fs is a waist of cpu time: |
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For example LZ4 will detect already compressed data (compression ratio |
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<12.5%), abort compression and store the file uncompressed. That's nice, |
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but it means that it has already compressed some blocks, before it could |
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measure it - waisting cpu time. |
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Greetings, |
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Daniel |
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-- |
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Get my PGP key at: |
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* |
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http://keyserver.ubuntu.com:11371/pks/lookup?op=get&search=0x837FB8B5BB9D4887 |
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* $ gpg --recv-keys --keyserver keyserver.ubuntu.com 0xBB9D4887 |
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