from_collapse_limit
No restart — settable per sessioncount (relations)
How aggressively the planner merges sub-queries into the parent for join planning.
What it does
from_collapse_limit controls when the planner stops pulling sub-query items up into the parent FROM list to consider them together. Like join_collapse_limit, it bounds the size of the join-ordering search to keep planning time sane.
How to tune it
Usually kept equal to join_collapse_limit (both default 8). Raise both together for complex analytical queries where a better global join order is worth extra planning time; the trade-off is the same.