testing for corruption

[Jeff Harrison]

--- Nancy Palmquist <nlp at vss3.com> wrote:

> Jeff,
> 
> I have seen corruption that falls into a few
> categories.
> 
> 1) a block of records is just bad, usually caused by
> a bad hard drive sector or 
> a FAT table failure that pointed to sector
> incorrectly.  In this case, the 
> records before and after the sector are just fine
> but the records that did live 
> in the sector are ruined.  They all need to be
> erased and returned to the free list.
> 
> 2) Corruption during a shuffle - Part of the file is
> structured be one map and 
> part by a second map.  I have seen this in more than
> one form.  A chunk of 
> records in the middle (usually when someone update
> the data during a shuffle) 
> or half right and half wrong.  When the file is
> increased, the shuffle will make 
> the new file in a new place.  When the shuffle is
> making the file smaller, it 
> writes over the existing file, from the beginning. 
> This crashes part way thru 
> and the data file is trashed.
> 
> 3)  Mismatches between key and data files as to the
> number of records each counts.
> 
> 4) this can also apply to the key,  keyx1, keyx2,
> keyx3 types of file layouts.
> 
> I have also seen cases where you can see the data on
> the screen but the free 
> record flag is set to free so the data is not seen
> by filePro.  That was a 
> bugger to fix.  Can not imagine how that happened in
> the first place, but I saw 
> it at least twice.
> 
> Sounds like a great tool, but corruption can come in
> a variety of forms.  Might 
> be tricky to figure out what is exactly needed.
> 
> Nancy
> 

Hi Nancy.  Thanks.  That it is still 2 votes to 1
against my developing this though - wait make that 2
to 2 as I would vote yes :-)

Yes, the utility that I am proposing would detect the
corruption from your #1, and #2 scenarios, as I would
expect to see non ascii data filepro's data fields.

As for #3, mismatches between # of records in key and
data - I don't think a utility is needed for that as
filepro will detect this for you.  dexpand will even
fix it for you as I'm sure you are aware.

Good point on #4 keyx1 datax1 x2, etc.  It would also
need to handle qualifiers I guess.

I have also heard of cases where the record is marked
as deleted, but there was still data there - although
a don't know that I have ever come across that myself.
 This utility would check for that.

Thanks for your comments.

Jeff Harrison
jeffaharrison at yahoo.com

Author of JHImport and JHExport. The fastest and
easiest ways to import and export with filepro. 


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