系統技術非業餘研究 » 推介xz高壓縮率演算法
這幾天看到Linux核心2.6.38釋出的release說明裡面提到:
The version .38 kernel comes with a library for decompressing XZ, a format developed from LZMA and known for its high levels of compression. This library is the basis not only for SquashFS, which now also offers XZ, but also for code that allows the kernel to unpack any parts of itself and of the initial ram disks (initrds) that were compressed with XZ.
覺得比較好奇, Linux下有那麼多的壓縮演算法, 為什麼要用這個, 它有什麼過人之處? 今天深入瞭解了下xz, 順便作了簡單的benchmark體驗了下.
官方網站在這裡
#我的機器配置
$ summary
...
# Aspersa System Summary Report ##############################
Date | 2011-03-17 10:24:13 UTC (local TZ: CST +0800)
Hostname | yufeng-laptop
Uptime | 1:46, 5 users, load average: 0.97, 1.03, 0.84
System | Dell Inc.; Latitude E6400; vNot Specified (Portable)
Service Tag | 9MKDW2X
Release | Ubuntu 10.10
Kernel | 2.6.38-yufeng
Architecture | CPU = 64-bit, OS = 64-bit
Threading | NPTL 2.12.1
Compiler | GNU CC version 4.4.5.
SELinux | No SELinux detected
# Processor ##################################################
Processors | physical = 1, cores = 2, virtual = 2, hyperthreading = no
Speeds | 2x2535.000
Models | 2xIntel(R) Core(TM)2 Duo CPU P8700 @ 2.53GHz
Caches | 2x3072 KB
# Memory #####################################################
Total | 1.95G
Free | 16.70M
Used | physical = 1.93G, swap = 4.42M, virtual = 1.94G
Buffers | 51.30M
Caches | 1001.72M
Used | 1.09G
...
#安裝壓縮軟體
$ apt-get install xz-utils bzip2 lzop
#準備資料
$ tar cf 1.tar linux-2.6.38 && cp 1.tar 2.tar && cp 1.tar 3.tar
$ ll 1.tar 2.tar 3.tar
-rw-r--r-- 1 yufeng yufeng 440494080 2011-03-17 18:17 1.tar
-rw-r--r-- 1 yufeng yufeng 440494080 2011-03-17 18:17 2.tar
-rw-r--r-- 1 yufeng yufeng 440494080 2011-03-17 18:17 3.tar
#開壓
$ time xz 1.tar
real 5m4.269s
user 5m1.670s
sys 0m1.340s
$ time bzip2 2.tar
real 1m3.357s
user 1m1.490s
sys 0m0.610s
$ time lzop 3.tar
real 0m5.526s
user 0m3.550s
sys 0m0.490s
#看壓縮結果
$ ll 1.tar.xz 2.tar.bz2 3.tar.lzo
-rw-r--r-- 1 yufeng yufeng 65092368 2011-03-17 18:18 1.tar.xz
-rw-r--r-- 1 yufeng yufeng 76103454 2011-03-17 18:19 2.tar.bz2
-rw-r--r-- 1 yufeng yufeng 151462273 2011-03-17 18:17 3.tar.lzo
#解壓還原
$ time xz -d 1.tar.xz
real 0m8.507s
user 0m6.390s
sys 0m0.670s
$ time bzip2 -d 2.tar.bz2
real 0m19.019s
user 0m17.420s
sys 0m0.670s
$ time lzop -d 3.tar.lzo
real 0m6.261s
user 0m1.610s
sys 0m0.610s
從上面的資料我們可以看出, xz的壓縮率確實不錯,解壓速度也飛快,就是壓縮比較慢,但是我們大部分的需求是讀,所以無所謂,一輩子壓不了幾次.
推薦在專案中使用,Linux都用了,我們怕啥!
玩的開心!
PS.
劉曉東 同學說:
剛剛在網上看到了一個XZ的並行版本pxz（http://jnovy.fedorapeople.org/pxz/），當然它的目的是為了加快xz的壓縮速度同時儘量小的改變xz原來的高壓縮率。
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