Migrate runner

Important notice: this code might be outdated, as it was back 9 months ago when we're using it. If you're interested in trying it out, write me and I'll update you with the latest code and examples probably. (I'd make it myself but... first, I have no enough time atm to tie up all loose ends and second I don't really know is this thing used by someone or no. /2017-08-28 @OnkelTem/

See also: https://www.drupal.org/node/2708723

This module allows to run migrations in batches and in multiple threads.

Example usages:

Single threaded, 100 items per batch:

  drush mr-i --group=my_group --batch=100

Multi-threaded, 100 itemas per batch, 4 threads:

  drush mr-i --group=my_group --batch=100 --threads=4 --config=modules/custom/migrate_runner

The --config option points to the module's directory for drush can consume drushrc.php from there which contains a customized version Drush Logger.

Its only purpose is to ignore error messages on SQL deadlocks. Without it you'll be probably getting loads of them thinking that something is broken while deadlocks are actually handled: there's a local version of MigrateExecutable class which restarts transactions in case of deadlocks. It's worth to say it's invoked only when you're using threads.