[Lustre-devel] [Fwd: feed api, rev2]

[Nathaniel Rutman]

Andreas Dilger wrote:
>
> With the change to force the "ONESHOT" behaviour, this hurts the ability
> of the userspace process to pipeline operations.  No matter how large a
> read the user process does, it will eventually have to finish processing
> ALL of the records before it can read any more, or they will be lost on
> the next read and any application failure will result in lost records
> if they are not completely processed.  I preferred the ability to
> explicitly cancel records.
>   
There are arguments on both sides.   I'd really like to stay away from 
having
multiple cancellation mechanisms though - I think this will be extra 
work and
extra confusion.
With explicit cancel and a regular file we can have multiple readers all 
reading the same audit log,
which is a big plus. (Record would be purged at first cancel.) This adds 
complication
for the users though, which is a minus: they must now a) persistently 
keep track of
their last-processed record ID, b) explicitly cancel records, c) map 
record numbers
to file offsets.  I think c) is a real hassle.
With explicit cancel and a FIFO we have a) and b), but not c), but not 
multiple
readers either.