GML download slow through postgis compared to local shapefiles

[Maarten Plieger]

Hello All,
Currently I am comparing GML download performance through a WFS with 
mapserver. The source data is stored directly on disk in the ESRI shape 
format, and is also available from a postgis database located on the 
same machine. So it is exactly the same data but from different sources. 
The shapefiles contain about 90000 polygons per file. I am timing the 
rendering time in WMS and the download speed in WFS.
WMS rendering time for a shapefile:
    For the shapefiles on disk:  2.897 seconds
    From the postgis database: 3.3 seconds.
(seems ok for both data sources)

However when I start downloading the data with the WFS in GML2 format:
For the shapefiles on disk:  8 Seconds
    66,8 MB in 8 sec
    8,35 Mb/Sec <== fast
 From the postgis database: 84 Seconds
    66.8 MB  in 1 min 24 sec
    800KB/Sec <== slow

These are the postgis parameters:
CONNECTIONTYPE postgis
CONNECTION "host=localhost dbname=pliegerdatabase user=plieger  
password=* port=5432"
DATA "the_geom from (select * from vcdtrop) as foo using unique gid 
using SRID=4326"

Why is downloading GML data through WFS from a postgis database 10 times 
slower than from locally stored shapefiles?
Can I do something to improve things? I am using mapserver 5.0.0-rc1 on 
SUSE.

Thanks in advance,
Maarten Plieger