temp_buffers
No restart — settable per sessionmemory per session (MB)
Per-session cache for temporary tables.
What it does
temp_buffers is a private, per-session buffer pool used only for temporary tables (not regular tables, which use shared_buffers). Each session that touches temp tables can allocate up to this much, on first use.
How to tune it
The default 8 MB is fine unless a session works with large temporary tables — then raising it (for that session) keeps the temp data in memory instead of spilling. Remember it's per session, so a high global value times many sessions adds up.