IOC does not pool network link PVs?

["Kasemir, Kay via Tech-talk" <tech-talk at aps.anl.gov>]

Hi:

Just noticed something unexpected.

Assume you have a first IOC generating data:

record(calc, "data")

{

   field(SCAN, "1 second")

   field(CALC, "RNDM")

}

With display tools like EDM, CS-Studio, …, no matter if a display shows “data” once or 100 times, the client pools its PVs, so the tool only has a single connection to the IOC, with a single channel for “data”.

When I use a second IOC to read the data, however, there seems to be no such pooling. For example, running this IOC ...

record(ai, "read1")

{

   field(INP, "data")

}

record(ai, "read2")

{

   field(INP, "data")

}

record(ai, "read3")

{

   field(INP, "data")

}

.. will create the channel “data” three times.

On the first IOC, the server report shows one connection and then the same PV name in 3 channels

epics> casr 10

Channel Access Server V4.13

1 client connected:

    TCP client at 10.159….

… 3 Channels

…

       Channel: ‘data'

            field_type=DBF_DOUBLE (8 bytes), dbr_type=DBF_DOUBLE, 1 element, no filters

            # on eventq=1, access=rw

        Channel: 'data'

            field_type=DBF_DOUBLE (8 bytes), dbr_type=DBF_DOUBLE, 1 element, no filters

            # on eventq=1, access=rw

        Channel: 'data'

            field_type=DBF_DOUBLE (8 bytes), dbr_type=DBF_DOUBLE, 1 element, no filters

            # on eventq=1, access=rw

We noticed this when checking network traffic for an IOC that monitors waveforms in a similar arrangement.

Note that the reading records don’t even need to be processed.

Each INP link creates a channel, a CA monitor is created, the same waveform data is sent multiple times.

As a workaround, you may update your database to insert a ‘mirror’ record like this:

record(ai, "mirror")

{  

   field(INP, "data")

}

record(ai, "read1")

{  

   field(INP, "mirror")

}

record(ai, "read2")

{  

   field(INP, "mirror")

}

record(ai, "read3")

{

   field(INP, "mirror")

}

Now, the first IOC will show only one channel for “data”.

I assume the IOC always behaved this way, and adding a PV pool would be a major change.

-Kay