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Subject: Re: asyn or caput rate limits?
From: Michael Davidsaver <mdavidsaver@gmail.com>
To: "Brown, Garth" <gwbrown@slac.stanford.edu>, "'tech-talk@aps.anl.gov'" <tech-talk@aps.anl.gov>
Cc: "Gang Huang \(ghuang@lbl.gov\)" <ghuang@lbl.gov>, "Carlos Serrano \(cserrano@lbl.gov\)" <cserrano@lbl.gov>, "Larry Doolittle \(ldoolitt@recycle.lbl.gov\)" <ldoolitt@recycle.lbl.gov>, "Ratti, Alessandro G" <ratti@slac.stanford.edu>, "Vamsi Vytla \(VKVytla@lbl.gov\)" <VKVytla@lbl.gov>
Date: Sun, 30 Apr 2017 18:27:49 -0400
On 04/29/2017 05:54 PM, Brown, Garth wrote:
>>>> for tag in range(2, 130):
> ...     print tag
> ...     epics.caput('RFS2:B15:SHELL_0_DSP_TAG_W', tag)


This client design  will *always* have a risk of dropping put values.
In fact this is part of the design of Channel Access, asyn, and the
EPICS database to avoid unbounded queue sizes.  If you can't tolerate
lose of put values then I think you'll need to address rate limiting at
the client/sender end.

Simply adding 'wait=True' to caput() will ensure that the client will
not send put requests faster than the server/IOC can process them.  This
will work the same with and without ASYN_CANBLOCK on the server end.

http://cars9.uchicago.edu/software/python/pyepics3/overview.html#epics.caput

http://cars9.uchicago.edu/software/python/pyepics3/pv.html#put-with-wait-put-callbacks-and-put-complete


References:
asyn or caput rate limits? Brown, Garth

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