6. Impact on DDS Domain
This section describes additional aspects of the Record and
Replay Service and its interaction with other systems.
6.1. Intrusiveness
Relevant characteristics of the Record and Replay Service
with respect to ‘intrusiveness’ for an existing system are:
- The service can be optionally configured on any DDS node in the system.
- When run as part of an existing federation of applications,
it utilizes the federation’s shared-memory segment to obtain
the data (so locally-published data is not required to travel
over the network to be recorded by the service, and vice-versa
for replaying towards co-located subscribers).
- When run on a dedicated RnR node, data to be recorded is
transparently forwarded to that RnR node, typically using
multicast network features (and so not inducing extra network
traffic).
- Services are controlled in ‘the DDS way’, i.e. a data-centric
way where command and status topics allow DDS-based ‘remote control’
over the service from anywhere in the system.
- A dedicated RecordAndReplay partition is utilized by RnR
to bound (contain) the control/status flows.
- In the case of a dedicated RnR node, this partition can be
configured to be a so-called ‘local Partition’ thus bounding
(containing) all control/status traffic to the RnR node.
- Replaying (subsets) of recorded data ‘by definition’ has impact
on an existing system:
- It can induce unanticipated traffic-flows towards subscribing
applications
- It typically triggers application-processing of such replayed
data...
- which can be considered ‘intentional’ and inherent to the
purpose of replaying recorded data
Summarizing, it can be stated that when dedicating a specific computing
node for Record and Replay and confining the control and status traffic
to control the service to stay ‘inside’ that node, recording of data
in a multicast-enabled network is non-intrusive.
Note that the few shared topic-definitions (definitions only, not actual samples of
these topics when these are ‘confined’ to the RnR node) that would be visible
system-wide when inspecting the built-in topics of the system (for instance with a
tool like the Vortex OpenSplice Tuner) are considered non-intrusive as they only imply a
small and static amount of data occupied by the related built-in topic samples.