Experimental Physics and
Industrial Control System

Matthias Clausen DESY -MKS-2/KRYK- <[email protected]> · Thu, 27 Feb 1997 10:53:53 +0100 (MET)

Chip writes:

>On the problem of getting data which is cached in an IOC to archive clients:

>1) no, there is nothing written down yet
>2) we plan to have the client ask the archive server, who will be
>   aware of the cache and ask the data source for it, and will then
>   return it to the client.  This keeps the clients small, and keeps
>   the load on the data sources small (one "client").

The question of written API functionality is not only related to cache but also to getting 
data from the archive server and/or to get data from the archive server to filter 
server(s) and to clients. The earlyer we agree on those the more realistic is the 
integration of existing applications.

The caching problem can be solved by either asking the IOC directly for those data or to 
trigger the IOC to send the cached data to the archive server.

Both ways seem to be necessary:
If a client directly asks the IOC for data you'll just read the whole cache and use what 
you need. I.e. if MEDM calls up a strip chart and you want to get the history displayed 
you can directly ask the IOC for cached data. ( the call -based on the archive record- is 
already implemented the integration in MEDM will follow)

If a client asks the archive server for data which is younger than those already archived 
the archive server will already have its monitors for the record setup and running so you 
only need to trigger the cache in the IOC to flush. The monitors will fire and the data 
will be tranferred the established way to the archiver. This way the client does not know 
where the data came from ( IOC-cache, archiver-cache, disk). Also this way is implemented 
for the archive record we use on the IOC.
One might discuss whether an archive (cache) record is better suited or a dedicated cache 
process on the IOC - but the functionality will be the same.

Matthias

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System