When is mono appropriate?

I saw indirect references to this in other posts but could use some exact guidelines. When do you compile as the old-style LSL and when do you use mono? What's the benefit/tradeoff of each?

Mono is particularly bad for attached objects: the delays involved in handing over a mono script from one sim to another are felt by everyone and are not trivial.

Mono is particularly good for scripts that have a lot of code or store large amounts of data, or need to run quickly.

There's more to it than that, of course, and with any luck we'll get a heap of posts on this thread arguing the finer details.

The most important thing to remember is that nothing is set in stone, this stuff is still very much a work in progress. Forget about absolutes, there are none. Test your scripts under both runtimes and use the one that works best for you now. Revisit your scripts when server updates come out, and see if things have changed, because they will.

A couple of odd points to watch about Mono:

A Mono-compiled script will revert to LSO if it is edited in Inventory. The script will have to be opened and recompiled again in Mono when it is active in an object. It's a small thing but it can be a real bummer if you are not aware that this happens. The script will remain in Mono if it is only copied to Inventory for copying to other objects.

Be careful taking an object back into Inventory after editing and saving a Mono script 'live': the script will often, but not always, have reverted to the previous version when it is rezzed again. I haven't seen this happen with LSO but just recently it caused me a terrific amount of trouble and confusion until I realised what was happening.

Is there a debug setting or something to change your default compiler? I'd like to change default to NOT mono.

There is a patch in JIRA for one somewhere. (there it is! http://jira.secondlife.com/browse/SNOW-378 ). Meanwhile, some of the alternative viewers have been picking it up. Cool and Emerald have it, at least.

(Ah but that won't help you for in-object scripts.)

I don't want to change the compile target for scripts saved in my inventory. I want to change which checkbox is checked by default, when scripts are saved in objects.

For that one you would have to flip the default in ;lpreviewscript.cpp, it's going by caps rather than user preferences.

question was mostly answered in another recent thread...

MONO has slow responses on sim crossings and rezzing, and those are sim related issues (adds to sim slowdowns). so temp rezzors, vehicles, and portable items (attachments, huds, NPV, etc) should probably use LSO for the sake of sim health.

MONO is great for processing heavy (math, searching, property updates), UTF support, and roughly 50% more raw storage space.

LSO may still be a better choice for small scripts, as far as sim memory impact and availability, but LL has given conflicting info in the past about this, so your guess is as good as mine (optimally, mono SHOULD be better in this regard)

Free Memory checks are more accurate in LSO, in MONO they are at the whim of the garbage collector which runs sim wide, not per script