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

Subject: Re: Archiver Appliance established multiple CA connections for one channel
From: Andrew Johnson <anj@aps.anl.gov>
To: <tech-talk@aps.anl.gov>
Date: Fri, 14 Apr 2017 10:44:51 -0500
Hi Lin,

On 04/13/2017 08:17 PM, Wang, Lin wrote:
> Actually, the default 10 TCP CA connections are acceptable and not the problem
> for us. The problem is that for example we have 366 channels in one IOC
to be
> archived, as reported by casr() on IOC shell, Channel Archiver
established one
> CA connection and accessed 366 channels in total, whereas Archiver
Appliance
> established 10 CA connections (fine for us) BUT accessed ~1692 channels in
> total, which I cannot understand.

I don't know for sure how the Archiver Appliance works, but from the
evidence you have posted it probably uses a configurable (default 10)
number of agent processes which connect to the IOCs. It probably also
has one or more master processes which direct requests for archiving
each individual channel to those agent processes at the appropriate
time. If an agent is directed to archive a channel that it hasn't yet
connected to it will make that connection at that time, so eventually I
would expect every agent to make connections to all 366 channels on that
IOC (i.e. up to 3660).

I admit I'm slightly surprised that it doesn't try to direct requests to
an agent that already has a connection to that channel, but presumably
the approach that Murali uses is more scalable (or maybe it does try,
but it can't always honour that). As Michael explained, the SLAC
installation solves the problem of overloading their IOCs with archiver
connections by making the archiver connect through a CA Gateway, which
coalesces all the connections from the agents into a single connection
to each IOC.

> epics> casr
> TCP 10.1.204.12:49088(carchiver): User="histdata", V4.11, 366 Channels, Priority=20  (This line is for Channel Archiver)
> TCP 10.1.204.41:39671(archappl): User="control", V4.13, 216 Channels, Priority=0
> TCP 10.1.204.41:39672(archappl): User="control", V4.13, 192 Channels, Priority=0
> TCP 10.1.204.41:39674(archappl): User="control", V4.13, 164 Channels, Priority=0
> TCP 10.1.204.41:39677(archappl): User="control", V4.13, 164 Channels, Priority=0
> TCP 10.1.204.41:39679(archappl): User="control", V4.13, 136 Channels, Priority=0
> TCP 10.1.204.41:39681(archappl): User="control", V4.13, 198 Channels, Priority=0
> TCP 10.1.204.41:39684(archappl): User="control", V4.13, 180 Channels, Priority=0
> TCP 10.1.204.41:39688(archappl): User="control", V4.13, 108 Channels, Priority=0
> TCP 10.1.204.41:39694(archappl): User="control", V4.13, 164 Channels, Priority=0
> TCP 10.1.204.41:39696(archappl): User="control", V4.13, 170 Channels, Priority=0
> 
> When I reproduced it in a VM on my laptop, I have only 3 channels to be archived
> in the IOC and there is actually no any other channel in the IOC, Archiver
> Appliance established 3 CA connections (fine as well) BUT accessed 3*8=24
> channels in total.
> 
> epics> casr
> TCP 127.0.0.1:33826(debian-8): User="wanglin", V4.13, 8 Channels, Priority=0
> TCP 127.0.0.1:33827(debian-8): User="wanglin", V4.13, 8 Channels, Priority=0
> TCP 127.0.0.1:33828(debian-8): User="wanglin", V4.13, 8 Channels, Priority=0

- Andrew

-- 
Arguing for surveillance because you have nothing to hide is no
different than making the claim, "I don't care about freedom of
speech because I have nothing to say." -- Edward Snowdon

References:
Archiver Appliance established multiple CA connections for one channel Wang, Lin
Re: Archiver Appliance established multiple CA connections for one channel Michael Davidsaver
Re: Re: Archiver Appliance established multiple CA connections for one channel Wang, Lin

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