mapserver initialization delays

[Scott Melby]

Hello -

I am pretty new to MapServer, so I apologize if I am re-hashing old 
material.  However, I am having a significant problem and am unable to 
find a "reasonable" solution documented anywhere.  I am running 
mapserver 4.6, and am serving a single layer that contains about 350,000 
points from a PostGIS database.  The layer has a GiST index on the 
geometry column.  The following request 
http://www.geonomy.com/cgi-bin/mapserv?map=/var/www/geonomy/geonomy.map&layer=geonomy_features&mode=map&dataFilter=geometry%20is%20not%20null 
will draw all points in my table into a 256x256 RGB PNG file.  The issue 
I am having is that MapServer can take up to 3 minutes to draw the image 
the first time it is called(after any delay of 30+ minutes with no 
calls).  Once that initial draw completes, subsequent hits draw in about 
9 seconds.  In my research I have found a page that indicates that this 
is due to MapServer initialization.  But the advice given there was to 
send a request that causes all map features to be drawn after setting up 
the server.... which has not solved my problems.  The delay does not 
appear to be tied to a particular client session... because hitting that 
same URL from another browser draws quickly if done within a few minutes 
of the initial query.  However, if I wait long enough (seems to be about 
20-30 minutes) the next request will once again take 2-3 minutes instead 
of 9 seconds.  Note: I don't believe that the issue is due to 
efficiencies of drawing the same image or accessing the same data 
repeatedly, because I have found that altering the dataFilter parameter 
(which is passed to a FILTER on the layer in the map file) causes the 
image to change, but does not significantly alter the performance 
(filters with less points draw more quickly, but still take a relatively 
long time for initial query if delay is long enough before it is 
called).  I have looked at the mapserver demo_init.html file and have 
added code to my servlet that periodically performs the following get 
http://www.geonomy.com/cgi-bin/mapserv?map=/var/www/geonomy/geonomy.map&layer=geonomy_features&program=/cgi-bin/mapserv&map_web_imagepath=/tmp&map_web_imageurl=/tmp 
request every N minutes (intervals of 1 minute - 10 minutes)... but, 
this does not change the behavior. 

I have also tried performing the following get at 1 minute intervals to 
try to avoid problems that could be caused by inactivity (such as the 
GiST index having to be reloaded from disk, or mapserver dropping its 
connection to PostGIS)..  In this case the GET request is being sent 
from a Java using a HttpURLConnection that is set to not use caches.  
Note: I have also tried adding a BBOX to this request to make sure that 
the GiST index is being used.  However, this does not fix the problem 
either.

http://www.geonomy.com/cgi-bin/mapserv?map=/var/www/geonomy/geonomy.map&REQUEST=GetMap&SERVICE=WMS&VERSION=1.1.1&LAYERS=geonomy_features&FORMAT=PNG&BGCOLOR=0xFFFFFF&TRANSPARENT=TRUE&SRS=EPSG:4326&BBOX=-115,30,-108,37&WIDTH=256&HEIGHT=256&reaspect=false&dataFilter=geometry%20is%20not%20null

Any help is greatly appreciated.

Thanks in advance
Scott