What's the best practice when using `pool` in a package?

[niheaven]

For instance, if I need to implement a connection pool within a package, how should I proceed?

Previously, I created pool::dbPool() in the .onLoad() function and closed it with reg.finalizer(), which worked well. However, adding more data sources would clutter the .onLoad() function. Also, how can I establish a connection to the database only when it's needed for the first time?

Furthermore, if I invoke the following function multiple times, will it create multiple connections in a single pool, or will it create multiple pools?

con <- function() {
  pool::dbPool(odbc::odbc(), driver = "Oracle Instant Client", dbq = "xxx", uid = "xxx", pwd = "xxx")
}

What would be the best approach in this scenario, or is there an example package that addresses this?

[hadley]

I think your initial idea makes the most sense to me (although I'd use .onUnload rather than reg.finalizer()). And I think if you set minSize = 0 then the pool will only create connections as you need them — the function you suggested will create multiple pools, which I doubt is what you want.

I'm not sure what your concern with creating multiple pools in .onLoad() is: you're going to have to put that code somewhere. If you're concerned with creating a bunch of pool objects, you might want to put them in a list.

[niheaven]

Thank you! Here is my scenario: I have multiple data sources required by various packages, and I want to centralize the connection methods in a single auxiliary package. This would allow me to connect to any of the data sources by executing functions such as dbcons::db_a() or dbcons::db_b(). This led to my initial question.

Alternatively, if I could utilize pool within an environment in the auxiliary package, is this a better option?

[hadley]

Hmmmm, in that case I'd be tempted to do something like this:

the <- new.env()

con <- function() {
  if (is.null(the$con)) {
    the$con <- pool::dbPool(odbc::odbc(), driver = "Oracle Instant Client", dbq = "xxx", uid = "xxx", pwd = "xxx")
    reg.finalizer(the, function(env) pool::poolClose(env$con))
  }
  the$my_con
}