[cbm-vic-20]

There's a common access pattern with object-relational mapping frameworks where an initial query will be used to get a list of ids, then an individual queries are emitted for each item to get the details of the items. For example, if you have a database table full of stories, and you want to see only the stories written by a certain author, it is common for a framework to have a function like

    stories = get_stories(query)

which results in a SQL query like

    SELECT id FROM stories WHERE author = ?

with the '?' being bound to some concrete value like "Jim".

Then, the framework will be used to do something like this

    for id in stories {
        story = get_story_by_id(id)
        // do something with story
    }

which results in N SQL queries with

    SELECT title, author, date, content FROM stories WHERE id = ?

and there's your N+1

[ComputerGuru]

This plagues (plagued?) pretty much everything to do with WordPress, from core to every theme and plugin developed.

[metadat]

Oh yeah, the ORM thing (common side-effect with DB query abstractions) - I must not have been fully awake. Cheers and thank you for humoring me, @cbm-vic-20!

[tehlike]

With orms, it can be easy, but also often fixed with eager fetching too.