Add support for migrate instrument (performance measurement)

Does anyone know the history about why this was not included?

Migrate was added to core in #2125717: Migrate in core: patch #1 → . There is one comment that mentions that instrument is not included #26 → but there was no response.

I asked chx about the history in Slack. He said that at the time the goal was core migrations, which is not the same architecture as Migrate in D7. So, this feature wasn't in their minds at all.

I'm leaning towards pushing this to contrib. I realize it would be difficult to implement in a new contrib module, but migrage_tools has its own MigrateExecutable and drush commands so a lot of this could be done there. The only issue is they would have to override MigrateExecutable::import(), which they don't currently do, so in the future core changes there would also need to be implemented in tools.

There's a few other issues here if we did do this in core, Wrapping SourcePluginBase::prepareRow() is useless, that's called from the actual source's prepareRow() where most of the heavy row preparation happens, but it wouldn't be counted here. You would want to wrap the actual $this->prepareRow() call in SourcePluginBase::next(). Wrapping the event calls could probably be done with two events with very high and very low weights instead of putting them in the executable. it needs tests, etc. While migrate_tools does have a set of druch commands, the core migration drush commands are in drush core, so if we did decide to do this here, we would want to add to the drush core commands, not the version in tools (well, both, probably) We will discuss again in the meeting tomorrow, but I'm leaning towards closing this, doing what we can in tools, and/or possibly adding additional hooks/events/something in core to allow this to be easier or more effective in contrib.

I am moving this issue from Drupal core to Migrate Tools. It will need a different implementation, so I am changing the status from NR to NW.

We discussed this issue at two of the weekly migration meetings:

• 📌 [meeting] Migrate Meeting 2023-03-02 2100Z Fixed
• 📌 [meeting] Migrate Meeting 2023-03-09 1400Z Fixed

Comment #9 summarizes the discussion. Let me repeat part of it: we will consider adding hooks or events to Drupal core in order to facilitate this feature, but first we would like to see how much of it can be implemented in a contrib module. We will also consider refactoring so that it is easier to override the core executable class.