enable_seqscan
No restart — settable per sessionboolean (on/off)
A debug toggle that strongly discourages — not forbids — sequential scans.
What it does
enable_seqscan doesn't actually disable sequential scans; it inflates their cost in the planner so much that any alternative is preferred. Like the other enable_* settings, it's a diagnostic switch — useful for asking 'could this query use an index?'.
How to tune it
Leave it on. Toggle it off briefly in psql (SET enable_seqscan = off) to test whether the planner could use an index; if a much better plan appears, the real fix is to add or correct the index — or to recalibrate cost parameters like random_page_cost — not to leave the toggle off in production.