Increase the number of "dart/melos runners" or "instances"

[christianruppert]

Hello,
first of all a big thank you for creating this tool - I was able to speed up our build time from 13 to 3 minutes. Awesome!

Now for my question, we have a project with roughly 10 packages (all local at the moment).
It seems like a major aspect of the increase in speed is due to "multiple runners" melos somehow uses.

We are only using a fraction of the features, mainly the following:

packages:
  - '*'

scripts:
    pub:
      run: melos exec -- "fvm flutter pub get"
    pack:
      run: melos exec -- "fvm flutter packages pub get"
    build:
      run: melos exec -- "fvm flutter packages pub run build_runner build --delete-conflicting-outputs"

Before using melos we were using scripts to execute these commands on all packages - resulting in e.g. nearly 3 minutes for the pub get / packages get due to startup and shutdown times of the script. The build command took around 10 minutes.

When running with melos it seems like the execution happens more or less concurrent - speeding up most stuff by a factor of 4.

My question - is there any flag within melos which configures how many processes to run in parallel?
I have the feeling on my machine it might be 4 instances running - is this defined by CPU count, or e.g. some general setting in Dart?

The actual build time will most likely not benefit so much from "spawning" more processes (still might give it a try) - but the pub get scripts might become even faster if its possible to increase the number of proccesses.

So maybe you can point me in the right direction (if you know what I am talking about) - maybe there is some setting in Dart or melos to increase the number of concurrent executions.

If not - even the current reduction is awesome, thanks a lot again.

Cheers,
Chris

[blaugold]

You can specify the concurrency melos exec uses with the --concurrency option. The default value is hard-coded to 5, but the CPU count might actually make more sense.

[christianruppert]

Just found the option - RTFM :-) But thanks for the quick answer, will play around a bit with this setting. Still awesome tool, really great work, Thanks again..

Its located here (for others)
https://melos.invertase.dev/configuration/scripts
scripts/*/exec/concurrency
Defines the max concurrency value of how many packages will execute the command in at any one time. Defaults to 5.

PS: Might be a good idea to link this doc from the https://melos.invertase.dev/commands/run section

But honestly, for this tool, it just makes sense to check the whole doc for all the stuff possible with it :-)

[christianruppert]

Actually, the "script" part is already a link within the "run" section, I was just to stupid to click it...