Re: dbLoadRecord or dbLoadTemplate

[Ralph Lange <Ralph.Lange@bessy.de>]

Hi Emmanuel,

Using dbLoadTemplate on the IOC to blow up template databases has two noticeable disadvantages compared to blowing up the templates on the host:

• You lose the ability to use macro substitution on the IOC. (Which your mail is about.)
• The process can be slow, as the template database is re-read from the file system for every instance. If the IOC uses remote shell or ftp access, this adds up to half a second or so for every instance. If you break things down to e.g. each single error bit being an instance of a template database, this can easily add up to minutes. (That's where we changed plans...)
  

We have changed all our IOC applications to blow up the templates on the host side. When doing this, you may leave unresolved macros in the database, which can be substituted at load time using the technique you are describing.

I would strongly suggest blowing up templates on the host side, as it gets you fast load times plus macro expansion on the IOC.

Personally, I would even go as far as setting dbLoadTemplate on the IOC to "deprecated" status. I don't see an advantage over host side expansion. (That might rather be a core-talk issue, though.)

Hope this helps,
Ralph

ps. There is absolutely no need to push your substitutions into the IOC's environment.

   dbLoadRecord(file.db,"deviceName=toto")

does exactly the same job. (Embedded spaces can still be used: enclose the substitution string with a pair of \"s.)


Emmanuel Mayssat wrote:

All, 
Most of you must be familiar with dbLoadRecord and dbLoadTemplate.
I like the first one because you can pass parameters which are not
necessarily hard coded (i.e. you can use the same db file for different
instances).

epicsEnvSet(DEVN,"toto")
dbLoadRecord(file.db,"deviceName=$(DEVN)")

I like the dbLoadTemplate because of the clarity, but then for each
device instantiation you need to create a complete substitution file.

Is there a way to do something like this:
dbLoadTemplate(file.sub,"deviceName=$(DEVN)")
Where the db files is generated and then parsed once again with macro
provided in command line?