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<== Date ==> <== Thread ==>

Subject: Re: Channel access and ca_element_count
From: Benjamin Franksen <benjamin.franksen@bessy.de>
To: tech-talk@aps.anl.gov
Date: Wed, 7 Oct 2009 14:01:14 +0200
Hi Andrew

On Mittwoch, 7. Oktober 2009, Andrew Johnson wrote:
> On Monday 05 October 2009 15:54:33 Benjamin Franksen wrote:
> > On Montag, 5. Oktober 2009, Andrew Johnson wrote:
> > > I agree with Michael in favor of changing the behavior so that when a
> > > client specifies COUNT=0 in its subscription, it is requesting a
> > > dynamic element count such that successive events may have different
> > > numbers of elements. However it should never be given more than
> > > ca_element_count() elements so it can always use that number to
> > > allocate data storage at connection time.  If at some time in the
> > > future we want to make it possible for even that number to be
> > > increased, this could be indicated to the client by a pair of
> > > disconnect/ reconnect events.
> >
> > I would be very happy if something like this could be done at the
> > database level i.e. for pv links between records.
>
> I agree we should implement this for PV links, 

Excellent!

> but I don't want to break
> applications that might rely on the existing behavior 

Sure.

> (can you remember
> what happens right now, do both DB and CA links zero-fill the elements
> beyond the current element count?).

I dimly remember I have gotten garbage in some tests when I erroneously 
assumed that dynamic sizing would 'just work' but I can't remember the 
details.

Thanks
Ben


References:
Channel access and ca_element_count michael.abbott
Re: Channel access and ca_element_count Benjamin Franksen
Re: Channel access and ca_element_count Andrew Johnson

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