Free Disk Necessary To Retructure A File

Sat Jul 26 16:48:07 PDT 2008

John,

Thank you much.  I never realized that's how it worked.  I always
thought if you had a 500mb file and you were adding 100mb to it, then
you would need 1.1gb free to do it.  I thought it copied stuff from the
"old" key file to a new bigger one, and then deleted the old key file.
Thus since there would be an instant in time where both the "old" key
file existed and the new one existed, just before it deleted the old one
I would need enough disk space for both.

This is really a case of the customer causing the problem.  I have been
telling them for (3) years that they must upgrade their server. 

Thanks again for the info.

Regards,

Scott

Scott Walker
RAM Systems Corp.
ScottWalker at RAMSystemsCorp.com
Ph: (704) 896-6549

-----Original Message-----
From: John Esak [mailto:john at valar.com] 
Sent: Saturday, July 26, 2008 7:31 PM
To: 'Scott Walker'
Cc: filepro-list at lists.celestial.com
Subject: RE: Free Disk Necessary To Retructure A File

Yes, 
In the case of *adding* characters to a file... you only need the entire
disk space available (including the original file) to be the size of the
"resulting" file.  so, if your file takes up 500MB and you have a 600MB
disk.... you can only add 100MB more to that file, however you do the
math. If you take the very same 500MB file and try to "remove"
characters from it... the program will break and your data will be
lost... and everything bad will happen, because in this case you would
need at least the size of the original file in free disk space *before*
you start the shuffle operation. 

Actually, in such a situation, I think filePro's free disk free check
would complain and say the re=shuffle could not be done, rather than
destroy your data, but I wouldn't chance this. :-)  Do the calculating
yourself first... or you will end up having to break out of the define
program, or carefully roll lback all of your changes. Yikes, it would
just be a hassle.

John

P.s. Even though with the "in-place" re-define thing you don't need a
duplicate size area of free space available as the size of your final
file to do a shuffle that adds characters... I would hope that you would
have a few extra bytes more than the final restructured size free for
safety's sake.  I don't know who safety is, but he likes extra on
everything.

John

> -----Original Message-----
> From: Scott Walker [mailto:ScottWalker at RAMSystemsCorp.com]
> Sent: Saturday, July 26, 2008 6:38 PM
> To: john at valar.com
> Cc: 'filePro_List'
> Subject: RE: Free Disk Necessary To Retructure A File
> 
> John,
> 
> So are you saying that if I had 10 million bytes free on my disk 
> drive, I could add a field to a file with 400mb as long as the 
> resulting file was not more than 10mb larger.
> 
> In other words, I don't need free disk space to be anywhere near the 
> size of the file I am restructuring.
> 
> Regards,
> 
> Scott
> 
> 
> Scott Walker
> RAM Systems Corp.
> ScottWalker at RAMSystemsCorp.com
> Ph: (704) 896-6549
> 
> 
> 
> 
> -----Original Message-----
> From: John Esak [mailto:john at valar.com]
> Sent: Saturday, July 26, 2008 6:32 PM
> To: 'Scott Walker'
> Cc: filepro-list at lists.celestial.com
> Subject: RE: Free Disk Necessary To Retructure A File
> 
> 
> <top posted question about file size in re-define>
> 
> You are right, You have plenty to spare.
> 
> I hate working in MB's... much better to work with the actual byte 
> size of the files and not worrry about converting to millions and then

> dividing by 1024*1024, etc.  If you simply  add 20 to the 2837 (which 
> you are heading for, (because the Define files program does not 
> display the extar 20 byte header needed for each record), giving you 
> 2857 and multiply this times 159,000 + 1 (for the extra 0th record 
> which is also commonly forgotten... you end up with 454265857 bytes of

> space needed to

> hold the new file... and that is really all you need.
> 
> Ken wrote the Define Files routine that adds characters, to do it "in 
> place". In other words you just move the end of file marker to the 
> highest point the file will require after the new full size is 
> calculated, and then writing all the records one by one from the end 
> of the file to their new position starting backwards from the end of 
> the file.  A nice, efficient way to make a file bigger back in the 
> days when disk space was at a huge premium.
> 
> So, you really have plenty of room for your addition.
> 
> If you were to *shrink* the file on the other hand (take away 
> characters from any field), this trick is not employed so you would 
> need the full new size of the file in free space, at least, for the 
> "temp" file which would be created and then moved into place.
> 
> John
> 
> 
> 
> > -----Original Message-----
> > From: filepro-list-bounces+john=valar.com at lists.celestial.com
> > [mailto:filepro-list-bounces+john=valar.com at lists.celestial.com] On 
> > Behalf Of Scott Walker
> > Sent: Saturday, July 26, 2008 3:25 PM
> > To: 'filePro_List'
> > Subject: Free Disk Necessary To Retructure A File
> >
> > I just want to make sure...
> >
> > I have a key file that is 436mb.
> >
> > I am going to restructure it, changing the record length from 2735 
> > to 2837
> >
> > I have 159,000 records in this file.
> >
> > I have 515mb of free disk space.
> >
> > I think I have enough disk space to do this.
> >
> > Am I right?
> >
> > Regards,
> >
> >
> > Scott
> >
> >
> > Scott Walker
> > RAM Systems Corp.
> > ScottWalker at RAMSystemsCorp.com
> > Ph: (704) 896-6549
> >
> >
> >
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