[Info-vax] naming convention in VMS MAIL

[Phillip Helbig undress to reply]

In article <1df3cd57-36c4-4771-9708-db6d8bdac9c4 at googlegroups.com>, Hein
RMS van den Heuvel <heinvandenheuvel at gmail.com> writes: 

> On Wednesday, December 19, 2018 at 4:25:53 PM UTC-5, Phillip Helbig
> (undress to reply) wrote: 
> 
> > VMS MAIL has files like MAIL$45870BB2000500B0.MAI;1.  The digits are not 
> > random, but are related to (at least) the date and time.  What is the 
> > exact format?  Has it changed in the last 25 years?
> 
> Hmm, I don't know why our friend Steve start to waffle about API's,
> opaqueness, performance and such. The question was highly specific.
> "What is the exact format". There is no suggestion Philips wants to do
> something useful with that. Perhaps just curious. 

Yes.

> Good links though. 

Yes.

A bit of background: Suppose I have filed a message but forgot where.
(Yes, there is MLSEARCH, and a while back Hunter was kind enough to make
it work on ALPHA, but I think it has a memory leak or something since if
it runs for too long everything freezes up.)  With DIR/SINCE/BEFORE I
can easily find the MAIL$* files from the time in question, and hence
the directory (I have very many mailfiles in a couple of dozen
directories.  This is what made me wonder about the format. 

> The format was once changes in the early 90's or so when the old linear
> date-time to name mapping was found to deliver horrible performance
> problems on mail 'purge' due to constant directory block shuffles as
> folks tend to delete old Email. The revised algorithm picked a 'middle'
> piece of the date-time as MSB somewhat randomizing external messages
> over the sub-directory, but potentially leaving horribly sparse
> directories. All that don't matter much. 
> 
> Below a piece of (sadly undocumented) DCL I wrote ages ago which has the
> core algorithm. The script finds 'missing' mail records in the MAIL.MAI
> indexed file opening it twice, once to scan, once to to lookups.  I know
> I have written a better description, but can't find is just now. 
> 
> The mail 'message key' is constructed as:
> 
> $mes="12345678"   ! Allocate 8 bytes
> $mes[48,16]=%x0005  ! Hard coded
> $mes[00,32]=F$CVSI(16,32,rec)  ! MSB form binary date-time
> $mes[32,16]=F$CVSI(48,16,rec)  ! LSB from binary date-time

Yes, that explains it.  Thanks!