Why a flat file?

Laurent Joncheray <lpj at merit.edu> writes
 * > Apart the usability by other people/programs (agrep covers a lot of 
 * > sins/scripts) the size of the dbm file
 * > is likely to be enourmous as well. Of course you can easily walk the
 * > whole dbm file and produce a readable version but the offset idea
 * > seems quick enough anyway so why bother ? 
 * 
 * 	What happens to the flat file when you do a delete or
 * update? What about the updated offset? How does the flat file look like
 * just before the cleandb job?

This is what happens at a delete:

- the object is looked up
- the reference in the dbm file to this object is removed (therefore
this object can no longer be looked up)
- the first attribute (*in: for networks) is replaced by (*XX:)
thereby not changing the file size and other offsets
- any new objects are ALWAYS appended to the file, and offsets added
to the dbm file
- at cleandb the bit that reads objects will automatically skip
objects that start with *XX, therefore removing all the old (removed)
objects.

An update is nothing more than a delete followed by an addition.

-Marten



-------- Logged at  Wed Apr 6 22:33:19 MET DST 1994  ---------