Here are my suggestions:
1. increase the WAL files setting. I think the usual setting is 0. I usually increase it to 3 or 4.
2. increase the sort_mem from 512 to 2048; this means "use up to 2MB RAM for in-memory sorting before dumping the data to disk and using the slower disk-based sorting routine". 512KB is not enough.
3. Check the fsync parameter - this varies by platform. Turning it off is less safe but faster.
4. Increase the shared_buffers setting.
5. Make sure you have some checkpoint_segments (number greater than 0) .
Remember to restart the server after each change and test. If using the pg_ctl program, check the actual logfile, since it has the bug that if the server exits due to a misconfigured .conf file it will still report success.
