Any time a migration is run, the code loops over every row in the source. There is no way to migrate an individual row, or a few selected rows.
There are some source plugins that cannot support anything better, but any source plugin that extends SqlBase should be able to access individual rows efficiently. There may be other sources that can also do this.
Using drush and the Migrate Tools module, try drush mim my_migration --idlist=123. The migration loops over all rows. If there are enough rows, then this can take a long time.
Provide an API that some source plugins can implement, allowing specific rows to be migrated.
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Add an API for selective migrations.
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The D7 migrate system has a great feature whereby you can import specific IDs, and not have to loop over all IDS in the source query. This is vital for speed when testing a migration and you need to test and entity that has a certain field or odd values. SQLBase should support that by looking for an 'idlist' and altering the source query accordingly. The first user of this feature will be the --idlist option of drush migrate-import (see migrate_plus module).
Needs work
11.0 🔥
Enhances developer experience.
It affects performance. It is often combined with the Needs profiling tag.
The change is currently missing an automated test that fails when run with the original code, and succeeds when the bug has been fixed.
A documentation change is requested elsewhere. For Drupal core (and possibly other projects), once the change has been committed, this status should be recorded in a change record node.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
#53 works great for me on drupal 10.2.3.
Thank you very much for fixing this issue (migrating one piece specific piece of content for debugging purposes used to take 16+ min, now it's done in a couple of seconds on a project I am working on right now).
Looking forward to seeing this merged into core.