For large dynamic responses generated by our application occasionally they are being buffered to disk

2008/01/29 14:21:13 [warn] 19297#0: *12289266 an upstream response is buffered to a temporary file /opt/local/var/run/nginx/proxy_temp/ 3/50/0000123503 while reading upstream, client: 4.224.132.81, server:
www.redbubble.com , request: "GET /people/redbubble/journal/206322-redbubble-post-card- everyones-an-artist HTTP/1.1", upstream:
"http://172.16.0.72:8005/people/redbubble/journal/206322-redbubble-post-card-everyones-an-artist ", host: "www.redbubble.com"

In this case the resource is

[dave@crimson ~]$ curl -I
http://www.redbubble.com/people/redbubble/journal/206322-redbubble-post-card-everyones-an-artist HTTP/1.1 200 OK Server: nginx Date: Tue, 29 Jan 2008 03:22:08 GMT Content-Type: text/html; charset=utf-8 Connection: keep-alive Set-Cookie: _session_id=223812df7b7e519d8ca3b2a6540b7016; path=/ Cache-Control: private, max-age=0, must-revalidate Content-Length: 73827

73827 bytes long (before compression)

I have

proxy_temp_file_write_size 128k

set to 128k, which I thought would buffer up to 128k of data in memory before writing it to disk.

Cheers

Dave