XOVER ranges

Russ Allbery rra at stanford.edu
Fri Apr 4 03:30:27 UTC 2008

"Jeffrey M. Vinocur" <jeff at litech.org> writes:

> So I'm writing to ask, what do we think of this behavior?
> It means if the client enters the group, then new articles arrive, then 
> the client does XOVER 1-, it does not receive info on the new articles.  
> More disturbingly, if the client does XOVER 1-100, and the old high 
> watermark was 80, the response reads "224 1-100 fields follow" but then 
> only data on articles up to 80 is supplied.  I'm not sure that any sane 
> client would ever actually encounter the latter, since it will also have a 
> stale idea of the high watermark until it reenters the group.
> I see three options:
>   (1) Ignore it
>   (2) Change CMDgetrange() to not adjust the watermarks
>   (3) Change the XOVER response line to echo back the adjusted watermarks
>       rather than the originals
> Thoughts?

I think 2 is clearly the right solution if all of the overview backends
can handle ranges outside the current watermarks.  However, I haven't
looked at any of the code for long enough that I don't remember how it

> P.S.  Russ, any thoughts about my original supposition?  

I'm not sure that I saw your original suggestion, unless it was in a
message that I replied to.  I thought I'd replied to all your mail.

>       I'm still worried there might be a bug lurking in the
>       unmap_file/map_file that can take place in the middle of the search,
>       since SendIOv may still have references to data in the old location.

Oh, yes.  Given that tradindexed advertises OVSTATICSEARCH false, it
shouldn't be doing that.  Good catch.  It either needs to advertise
OVSTATICSEARCH true to force nnrpd to copy the data or it needs to never
remap in the middle of a search.  I think the latter is more correct.

That may require other changes to not remap the index file in the middle
of a search either.  We really should only remap the files at the time of

Russ Allbery (rra at stanford.edu)             <http://www.eyrie.org/~eagle/>

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