ietf-nntp Backfill

[Taz Higgins]

As another client author (Virtual Access), backfilling is a complete and 
utter pain at the server end.  Article numbers are monotonically increasing 
and unique.  

Anything else causes more queries and information to have to be sent by 
both client and server to cope with the variety of cases - this is to my 
mind "a bad thing" if no "a very bad thing"

to address the points clive raised


> [Q1] When a group becomes the current group, is the set of articles made
> available to the client fixed at that moment ?

Yes.  I would expect to look for artie numbers withing that range only. 



> [Q2] When will new articles become available and expired/cancelled ones
> become unavailable ? Is it:
>   - not until a new NNTP session
>   - next time the group is made the current group after another group
>     has been the current group
>   - next time the group is made the current group, whether or not it


I wouldn't expect that any article in the range would be there - the only 
ones that I might still expect to be there are the min and max articles - 
but even then I wouldn't assume so 
I wouldn't assume a client process such as reading articles could stop a 
server from expiring/cancelling articles 

repeatedly doing next's I wouldn't be surprised for more articles to appear 
with a number greater than that returned by group - although we'd stop 
asking at that point


> [Q3] Can an article appear with a number higher than the previous
> maximum, such as 1357 ? Obviously the new maximum would be higher 

yes 

> [Q4] Can an article appear with a number less than the previous minimum,
> such as 1111 ? Obviously the new minimum would be lower 

No 

> [Q5] Can an article appear with a number between the previous limits,
> such as 1250 ?

No 

> [Q6] Can the lowest numbered article disappear ? Obviously the minimum
> would increase if necessary 

yes 

> [Q7] Can the highest numbered article disappear even though a lower
> numbered article (such as 1266) remains ? Obviously the maximum would
> decrease if necessary 

yes 

> [Q8] Can any other article disappear even though a lower numbered
> article remains (e.g. 1266 disappearing with 1234 remaining) ?

yes

> [Q9] If an article disappears, can it ever reappear again ? The same
> article, this is, not a new article given the same number by the server,
> which we all assume is not permitted 

Yes - but only as it is the same article, otherwise article numbers must be 
unique 


> There are three common scenarios posited for NNTP clients and servers. I
> call these "monotonic", "backfilling", and "wind-back". They answer the
> first three questions:
> 
>                    Q3  Q4  Q5
> Monotonic          Y   N   N
> Backfilling        Y   N   Y
> Wind-back          Y   Y   Y
> 
> Servers appear to exist of all three kinds, but all clients I am aware
> of that use article numbers at all are monotonic 

VA is monotonic 

> A sensible client needs to allow for the user wanting to mark articles
> as unread. Therefore it must be able to cope with the backfilling
> strategy, by (for example) maintaining a list of ranges. Given this,
> there seems little reason to require that servers be monotonic 

I disagree strongly on this point - the read/unread status of an article is 
NOT stored on the server - that is a property of the client and it's 
display.  The server would have to store a list of what articles had been 
read by what client - this would add to the servers load tremendously - 
take a look at COmpuServe which does this, it's one of the reasons 
compuserves forums can be slow 

Articles can be pulled one by one as specified by the client using the 
references - let the client worry about this 






-- 
Taz Higgins of Ashmount Research
Virtually Accessing the Net with V I R T U A L  A C C E S S