[hero-24]

From my experience, planning is often the first headache I have to deal with (join order, hash sizing, operator choice), before concurrency and memory even come into play.

[exagolo]

You mean the "execution plan" for your queries? Ideally, those types of decisions are automatically done by the database.

[hero-24]

ideally? yes. in practice? big nope.

How you actually interpret what you're seeing here? does it look like more like optimizer fragility (plans that assume ideal memory conditions) or more like runtime memory management limits (good plans, but no adaptive behavior under pressure)?