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Java Forum / General / April 2007Compression used in Sun's JDK/JRE downloads?
How does sun get their compressed archive of Java binaries down to 15MB? When I uncompress these and then 'zip' or 'tar czf' the resulting file is 25MB, even using maximum compression flags. NM > How does sun get their compressed archive of Java binaries down to 15MB? > When I uncompress these and then 'zip' or 'tar czf' the resulting file > is 25MB, even using maximum compression flags. Since 1.2.2(?) they have something similar to pack200. If you were to dig up a copy of 1.2.1, you should find it much larger. Instead of individually compressing a large set of files each with duplicate data (signature strings, for example), a single file is produced that shares data between classes. This file can then be compressed as a single stream. For more information, google 'pack200'. Tom Hawtin >> How does sun get their compressed archive of Java binaries down to 15MB? >> When I uncompress these and then 'zip' or 'tar czf' the resulting file >> is 25MB, even using maximum compression flags. > >Since 1.2.2(?) they have something similar to pack200. If you were to >dig up a copy of 1.2.1, you should find it much larger. Doesn't look like they're using the pack200 distributed with the jdk, that creates archives that are 48% of original size. No real difference from gzip. Sun's jdk.*.bin downloads are 39% of the original size. The only tool does better is lzma, which creates archives that are 34% of the original size. # sh jdk-1_5_0_11-linux-amd64.bin && du -bs jdk1.5.0_11 113483747 jdk1.5.0_11 # jar cMf jdk1.5.0_11.jar jdk1.5.0_11 && du -bs jdk1.5.0_11.jar 55557396 jdk1.5.0_11.jar (49% of original size) # tar czvf jdk1.5.0_11.tgz jdk1.5.0_11 && du -bs jdk1.5.0_11.tgz 54730784 jdk1.5.0_11.tgz (48% of original size) # pack200 -J-Xmx500M -S-1 -E9 x.pack.gz jdk1.5.0_11.jar && \ # du -bs x.pack.gz 54622334 x.pack.gz (48% of original size) # du -bs jdk-1_5_0_11-linux-amd64.bin (Sun original) 43930095 jdk-1_5_0_11-linux-amd64.bin (39% of original size) # tar cvf - jdk1.5.0_11 | lzma -9 > jdk1.5.0_11.tar.lzma && \ # du -bs jdk1.5.0_11.tar.lzma 39714345 jdk1.5.0_11.tar.lzma (34% of original size) Since Sun's shar files contain self-extracting SFX archives they must have some custom software that can be decompressed with gzip/unzipsfx. NM >> Since 1.2.2(?) they have something similar to pack200. If you were to >> dig up a copy of 1.2.1, you should find it much larger. [quoted text clipped - 4 lines] > # du -bs x.pack.gz > 54622334 x.pack.gz (48% of original size) I'm not particularly surprised pack200 on the installer doesn't work too well. It's not going to comprise of all the class files in a ready to run state, so pack200 wont help. Running it on rt.jar might give you better figures. Also, IIRC, the JDK contains some debugging info (such as line numbers) whereas the JRE does not. Presumably there is not a great deal of point optimising pack200 to deal with debugging information efficiently. Tom Hawtin Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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