At present it is possible to retrieve data for a PV which is no longer archived, a "retired" PV, by specifying a template PV whose PVTypeInfo can be used instead. This is the retiredPVTemplate parameter. There are some drawbacks to this approach:
It is not always straightforward to determine a suitable Template PV
There is no implementation in the CS Studio databrowser to provide this parameter, and it is an extra complication for other clients
We have a proposal for a simpler mechanism. We observed that the only information used from the PVTypeInfo is the location of the data stores to be searched (the type itself comes from the PB files). The location of the data stores can be found instead from the policies.py file. The proposed change is:
If a PV is requested for retrieval, but its PVTypeInfo is not found (ie it is not currently being archived), then run determinePolicy from policies.py to get the locations of the data stores.
Then use these locations to search for data, and return it if found
This means that the client does not need to specify any extra parameters in order to retrieve data for a retired PV. This has been tested in our local test server and has the desired effect. Retired PV data can be retrieved from CS-Studio without any changes in the client.
This behaviour aims to be transparent to those not using it -
If retiredPVTemplate is specified then this will be used instead;
The behavious is enabled by a preference
We welcome feedback on this approach. In particular, others may have different uses of their policies.py file which may need to be accounted for.
aawdls
commented
2 years ago
At present it is possible to retrieve data for a PV which is no longer archived, a "retired" PV, by specifying a template PV whose
PVTypeInfocan be used instead. This is theretiredPVTemplateparameter. There are some drawbacks to this approach:We have a proposal for a simpler mechanism. We observed that the only information used from the
PVTypeInfois the location of the data stores to be searched (the type itself comes from the PB files). The location of the data stores can be found instead from thepolicies.pyfile. The proposed change is:PVTypeInfois not found (ie it is not currently being archived), then rundeterminePolicyfrompolicies.pyto get the locations of the data stores.This means that the client does not need to specify any extra parameters in order to retrieve data for a retired PV. This has been tested in our local test server and has the desired effect. Retired PV data can be retrieved from CS-Studio without any changes in the client.
This behaviour aims to be transparent to those not using it -
retiredPVTemplateis specified then this will be used instead;We welcome feedback on this approach. In particular, others may have different uses of their
policies.pyfile which may need to be accounted for.