random i/o and relative efficiency

For what I'm doing at the moment, it's academic, but I'm curious anyway.

I'm working on a program that needs to access most of the records in a file
for a given partial key.  There are about 100 records for each partial key
and of those, about 80 are "interesting."  All of the records that need to
be skipped are in the first quarter of the range for a given partial key;
the remainder are contiguous.  I've noticed that other programs that use
this file will chain to the 5 to 10 "interesting" records in the beginning
of the range and then chain to the first "interesting" record in the
contiguous part of the range, processing the remainder of the records in a
reade loop.  Is this faster than chaining to the first record that matches
the partial key and reading every record (chain--reade loop) processing only
the "interesting" records using simple logic?  The program I'm working on is
interactive and only reads 100 or so records for each screen, so performance
really isn't an issue.

I guess the real question is what is the performance difference, if any,
between a chain and a reade, or how many reades make a chain? 

Joel Fritz x1568

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