mapserver initialization delays

[Stephen Woodbridge]

Scott,

What you are likely seeing is the fact the the first long draw is that 
postgres is finding all you data and it is getting cached in memory. So 
the subsequent requests are all fetching the data from the cache. If you 
wait more and more of the data gets bumped from the cache.

There is very little mapserver specific startup costs. You might have 
read about database connection costs and pooling, but that is not what 
you are seeing.

-Steve W.

Scott Melby wrote:
> 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
>