mike ledoux writes regarding compressing a dump a chunk at a time:
> Oh, I'm not saying that it won't work, I'm sure it works just fine.
> I'm just skeptical that you get enough compression with this method to
> be worth trying to compress the data at all.
While it is almost always(*) true that the sum of the
individually compressed chunks will be larger than the compressed
version of the whole, it can get close enough that most of us don't
care. It's usually a question of what chunk size you use, and how
much state the compression algorithm maintains. It's been about 5
years now, but the last time that I looked at the gzip sources, the
size of the look behind buffer was either 4k or 8k. (I don't remember
which. I was looking at another scheme at the time and it used the
other size.) If you use small chunks (512 byte floppy blocks or 1K
filesystem blocks would be absurd), then yes, compression is probably
horible. If you use 1M blocks, on the other hand, and the first 4k
doesn't compress very well, but the later stuff works fine, then the
difference in overall efficiency may be(*) insignificant.
* Whenever I hear or say something absolute about compression, it's
usually not long afterwards that I come across a data set that is a
counter example. Such is the nature of depending upon the statistical
nature of the data to be compressed.
Bill
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