Re: dynamical record loading/unloading and normal database

[Andrew Johnson <anj@aps.anl.gov>]

Liyu, Andrei wrote:
> - at beginning, st.cmd load records by dbLoadRecords function. 
> - after all dbLoadRecords st.cmd calls IocInit(). 
> But I didn't meet in IOC and didn't read in manuals that IOC can load
> and unload record during its work (after initialization). 

That is correct, the current design for the database code does not permit 
records to be loaded after iocInit() had been called, nor can you delete 
records after iocInit().  To add this functionality will require quite a 
lot of work, and none of the EPICS users have wanted it sufficiently badly 
to put in the manpower necessary to implement it yet.

> If I am right maybe these items will appear soon?

No, nobody is currently working on this, and doing so while remaining 
backwards comptibility with existing device support would be impossible. 
There might also need to be changes made to the Channel Access protocol to 
implement record deletion.

There are several ways to work around this problem: The simplest is to 
load all of the records for all the functionality you will need in this 
run into the IOC, but disable (SDIS field) those parts of the database 
which are currently not operational or not required -  records that are 
not processed only take up IOC memory space, not CPU time.  Alternatively 
(if your network bandwidth allows this) you could implement just the I/O 
records in a vxWorks IOC and perform all of the control tasks in a soft 
IOC, which can easily and quickly be stopped and restarted with a 
different set of records.  If network bandwidth would be a problem then 
you could of course just have several alternate startup scripts for the 
same vxWorks IOC and reboot it using a different script to change the 
functionality it provides.  This would require that you be able to perform 
bumpless reboot on that IOC, but that is generally a solved problem.

- Andrew
--
There are 10 types of people in the world:
Those who understand binary, and those who don't.