[wulczer]

One of the important reasons Postgres connections are serviced by a separate process is that if that process segfaults, you only disconnect other connections (because if might have tainted shared memory when it died), but the main database process keeps running and you can reconnect immediately.

[adamtj]

Not quite. If a backend segfaults, postgres will detect it and immediately terminate all connections and exit. When it restarts, it will enter recovery mode. It does this because a segfaulted backend may have corrupted shared memory. The only way to fix that to restart in recovery mode and replay the WAL.