Question

I implemented an otp system using gen_server and gen_fsm. There is a configuration file to be read for some values that the software needs in order to run, an example may be:

{values, [value1, value2, value3]}.

I used a macro to extract one of these values

define(VALUES, my_utility:get_conf_value(values)). 

The question is the following: since ?VALUES may be called very often, and therefore the configuration file is parsed many times, should I embed ?VALUES inside the state of my gen_server of gen_fsm and extract it with a call any time I need it?

In fact I really appreciated the previous implementation because one could change the behaviour of the software just by changing the values inside the configuration file, without any #state{} change or call.

Which solution do you prefer?

Answer 1

The solution will depend upon your requirements. Performance vs “correctness”.

A possible solution would be to keep the configuration in a process state and re-read it regularly (checking if the file modification time has changed). This might be a good compromise between the two worlds.

Summary:

• Re-read from file everytime: always up to date, but slow with unnecessary IO
• Re-read on interval, store in process state: fast to read, but lagging behind
• Manual re-read: fast to read, but lagging behind and needs manual trigger
• Read once and store in process state: fast to read, needs restart to update

Requirements not considered: security, stability (corrupt config file?)