Re: Data Compression

["John C. Peterson" <jaypee@netcom.com>]

On Tue, Feb 01, 2000 at 09:33:17AM +0100, Jacco van Schaik wrote:
> On Mon, 31 Jan 2000, Jerome Kaidor wrote:
> 
> >    When you use a compressor like gzip, you tell it:
> > 
> >   "Here is a file, or data area for you to compress.  Here's where it
> > starts, here's how long it is.  Put the compressed version over there.  Come
> > back when you're through."
> > 
> > [...snip...]

   A general comment about database compression. Note that in the
case of the fplan databases, the records are padded to fixed lengths so
that a binary search can be used for the lookup by identifier. (See
Knueth or other texts for a description of the algorithm). The binary
search is *very* fast compared to a simple search by sequential read.
This is one feature that made fplan quite unique when it first came out
in 1989. It actually ran *fast* on the PC's of that era...

  The problem with runtime de-compression is that fseek() is not
fast (or even possible?) and it is crucial in the implementation of
any fast search algorithm. My point is that you probably don't want to
bother with compression on a desktop setup where disk space really
isn't an issue.  The speed penalty you would pay by giving up fast
searching algorithms isn't worth the space savings in a world where
5-10 GB drives are common place. Of course, it DOES make sense if we
are talking about a handheld or other environment where space is a
premium. Just my $0.02 ....

Regards, John

-- 
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