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JMStranz

DDS Reliable communication and writer history cache (WHC)

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In my application I'm using the topic QoS "RELIABLE".

In unfavorable network conditions, I receive the warning "writer ... waiting on high watermark due to reader".

Is there a way for the application to be notified about this event?
Note: I use the "ISO C ++ 2 DCPS" API and the "standalone" deployment.

Can I influence the behavior of the WHC via API functions (for example changing the value for the watermark)?

Thanks for your help in advance!

Best regards,
Jan-Marc.

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Hi Jan-Marc,

Thats 2 questions :)

  1. applications can exploit KEEP_ALL writer-history QoS setting which allows them to specify a timeout on the ability to 'get rid of their data' (i.e. to get notified of such a timeout when blocking on a high-watermark)
  2. the WHC settings can NOT be influenced by API-functions (as the whole point of DDS is to 'shield' applications from those underlying network intricacies) but you CAN choose to change the (default) settings (of a 100 kb watermark) like this (see 'Watermarks' section):
        <DDSI2Service name="ddsi2">
            <General>
                <NetworkInterfaceAddress>AUTO</NetworkInterfaceAddress>
                <AllowMulticast>true</AllowMulticast>
                <EnableMulticastLoopback>true</EnableMulticastLoopback>
                <CoexistWithNativeNetworking>false</CoexistWithNativeNetworking>
            </General>
            <Compatibility>
                <!-- see the release notes and/or the OpenSplice configurator on DDSI interoperability -->
                <StandardsConformance>lax</StandardsConformance>
                <!-- the following one is necessary only for TwinOaks CoreDX DDS compatibility -->
                <!-- <ExplicitlyPublishQosSetToDefault>true</ExplicitlyPublishQosSetToDefault> -->
            </Compatibility>
            <Internal>
                <Watermarks>
                    <WhcHigh>800 kB</WhcHigh>
                </Watermarks>
            </Internal>
        </DDSI2Service>

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