Messages in this thread | | | Date | Tue, 29 Jul 1997 08:54:39 +0200 | From | Rogan Dawes <> | Subject | Re: undelete? |
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On Mon, Jul 28, 1997 at 01:25:46PM -0600, Tim Bird wrote: > > > Now, solve this one, you open the file read/write and you start changing > > > the file in random places. Since even changing one byte will change the > > > compression dynamics you end up re-compressing/re-writing everything > > > following the position at the write(), block compression or no... I > > > challenge you to code that efficiently. > > > > My experience with computers indicates, that most activity comes in > > bursts, we therefor should not try to compress on the fly when the CPU > > has better things to do [unless it reduces IO and that's the current > > bottleneck]. We should rather store the uncompressed data and > > compress it later when we're in need of disk-space or have nothing > > better to do. [...] > > This is how NetWare does it and it works quite well. It is very nice > to have the compression and decompression performance requirements > decoupled. NetWare implements an asymetric algorithm that sacrifices > compression speed (which is done at off-peak periods) in exchange > for blazing decompression speeds. In this regard, NetWare actually > gets a double win. Compressed files not only take less space on > disk, but are served faster from the file system than uncompressed > files (because the decompression is so fast, and less disk blocks > are read.) > > Tim Bird
Folks interested in this might want to check out the LZO compression/decompression routines posted recently to c.o.l.a : real-time decompression, pretty fast compression, GPL, etc.
From the announcement :
LZO implements a number of algorithms with the following features: - Decompression is simple and *very* fast. - Requires no memory for decompression. - Compression is pretty fast. - Requires 64 kB of memory for compression. - Allows you to dial up extra compression at a speed cost in the compressor. The speed of the decompressor is not reduced. - Includes compression levels for generating pre-compressed data which achieve a quite competitive compression ratio. - There is also a compression level which needs only 8 kB for compression. - Algorithm is thread safe. - Algorithm is lossless.
Rogan -- Rogan Dawes rdawes@jhbelec.co.za Tel: (011) 490-7379 Fax: (011) 490-7327 - The software said it requires Windows 3.1 or better, so I installed Linux -
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