Re: MODSEQ in CONDSTORE

[Dave Cridland <dave@xxxxxxxxxxxx>]

On Wed Feb  1 23:20:18 2006, Mark Crispin wrote:
> I know that it's probably much too late to complain about this now, 
> but can someplace please explain why the MODSEQ is a 64-bit value?  
> Is there any serious possibility of there being more than 2^32 
> STOREs being performed on a single message in a mailbox?
Two stores on different messages generate two different MODSEQ 
values, though. So if it were 32-bit, then just filling a mailbox 
would be enough to exhaust it. You actually only need 2^32-1 STORES 
on a single message - the arrival of the single message itself 
increments the MODSEQ.


> The examples imply MODSEQ as a date/time, but as the document says 
> you can't actually do that.
Indeed, but it's possible to come close. ACAP uses modtimes that 
can't actually be times, they just look remarkably like them.


> What's more, I didn't observe any definition in the CONDSTORE 
> document of what is supposed to happen if a STORE results in no 
> change.
I don't think there's anything which states explicitly that if a 
STORE results in no change then no MODSEQ increases happen, but I'd 
assume that was implicit in the definition.


> I am implementing a new mailbox format which has a per-message 
> modification sequence.  For my purpose, it's easiest to have it be 
> monotonically increasing.  Also, I don't want to change it if STORE 
> results in no change.  I was going to make this available as a 
> MODSEQ for a possible future CONDSTORE implementation, but I see no 
> point in keeping it as a 64-bit value other than bloating the data 
> structures further. I want to see if I am missing something.
FWIW, Ken Murchison's patch for Cyrus can use a 32-bit MODSEQ value. 
There's nothing *forcing* the value to be 64-bit for servers, but if 
you overflowed a 32-bit, you'd have to reset the UIDVALIDITY in order 
to recover.

Clients, of course, have to deal with it as a 64-bit unsigned integer 
for all servers.

Dave.
--
          You see things; and you say "Why?"
  But I dream things that never were; and I say "Why not?"
   - George Bernard Shaw