Derive Clone for DatabaseOptions

[petoknm]

I am trying to port r2d2-mongodb to use this new mongodb driver and it would be very nice if DatabaseOptions could be cloned.

[saghm]

It definitely makes sense to make DatabaseOptions implement Clone; I've authorized our CI to run for this patch, and will merge it once it passes.

Note that wrapping this driver with r2d2 is probably not a good idea; it implements connection pooling under the hood, following the MongoDB CMAP spec. This means that making an r2d2 pool of Client (and by extension, of Database or Collection) will create a connection pool for each one, as well as all of the background threads that the driver needs for not only the pools but also to monitor the topology. The Client type implements Clone and Send, meaning that the best way to use it is to create one and then make a copy for each thread you spawn.

[petoknm]

Thanks @saghm. Yea, I was wondering that that might be the case when i saw the max_pool_size/min_pool_size options.

[saghm]

The old version of the driver actually had connection pooling too; it was written before the CMAP spec existed though, and we never got around to implementing the options that are now part of the spec.

[saghm]

The MacOS failures are due to a bug in our CI (not due to anything in the driver), so I'll merge this now. Thanks for the contribution!