Mark,
some things that come to my mind:
1. Mapserver's query mechanism is quite inefficient against database
sources (two pass, and pass by id to get the actual record, so for every
feature in your resultset a SQL statement is executed against the DB).
So I am not surprised about your query performance, I have had the same
experiences. What USING UNIQUE clause are you using in your MAP file,
and can you check that this pass by ID is indexed in the database?
2. You could try Mapserver as a Fast-CGI since connection overhead could
be an issue
3. You could also get Mapserver to output the XML (i.e. GML) of a
FeatureCollection if you would use the Mapserver WFS interface. Then
using an XSLT you could create your HTML table. Maybe this is faster,
but it still suffers from 1. ofcourse.
Hope this helps.
Best regards,
Bart
Mark Adams wrote:
Hi All,
I’m looking for ideas and explanations regarding performance when
publishing maps from ArcSDE and Oracle Spatial, and also with
displaying attribute data from these data source. We have been working
for a while now with from these formats through MapServer and PHP
mapscript, and have found the performance has been disappointing.
Specifically, we are trying to use Oracle Spatial (9i) as well as
ArcSDE against both Oracle and SQL Server (we gave up entirely on MS
Access personal geodatabase through OGR). Generally speaking we’ve
found that map draw operations are substantially slower with these
data sources than if we use Shapefiles; and that the performance hit
is even greater with drawquery operations, especially as the size of
the selected feature sets increases.
We did some informal testing, both within our MapServer environment to
compare the performance with different data formats, and also between
MapServer and ESRI ArcIMS environments. Here are some of the results
we came up with:
1. We compared MapServer performance with SQL Server ArcSDE and
Shapefiles (with spatial indexes defined for the Shapefiles), with a
large polygon layer representing property parcels (329870 records). To
draw the whole layer at full extents, it took 10 seconds with
Shapefiles, 26 with SDE. To zoom in to a small area, 0.3 seconds with
Shapefiles, 2.2 seconds with SDE. These times are just the draw times
reported from the debugging.
2. We compared MapServer performance with Oracle Spatial 9i Standard
Edition and Shapefiles, using a polygon layer that has about 6000
records. To draw the whole layer at full extents, it took 0.29 seconds
with Shapefiles, 0.98 with Spatial. To zoom in to a small area, 0.28
seconds with Shapefiles, 0.6 seconds with Spatial. We also tested
selected and highlighting features: select 75 records (querybyrect),
0.5 seconds with Shape, 2.7 with Spatial; select 3000 records, 0.5
seconds with Shape, 9.4 with Spatial.
3. We compared MapServer performance with ArcIMS performance using the
same data sources (the property parcel layer with 329870 records).
This is an even more informal test as we didn’t have access to the
same debugging info on the ArcIMS side, so I will just say that
comparing with Shapefiles only, the 2 platforms were roughly
comparable; but ArcIMS speeds up a little with SDE, while MapServer
slows dramatically with this format.
4. We have even more problems when we want to use the results from the
selection in test 2 to show the attribute data to the user on a
separate HTML form. On the ArcIMS side we can process attribute data
quick quickly as the server sends back an XML file with the attribute
data in it. On the MapServer side the only way we know to publish the
attributes is to loop through each field of each returned record to
create the HTML table. Extracting the data in this fashion is again,
for some reason, way faster with Shapefiles as the selection sets get
bigger – for example with the 3000 record test it took 3.2 seconds for
Shapefiles, and 9.4 seconds with Oracle Spatial. When you add those
times to the draw times the Oracle Spatial approach becomes
unworkable; likewise with ArcSDE.
So, there are some questions in all this that I’m hoping the experts
on the list can answer: are we doing something wrong, or are these
numbers to be expected, and if the latter, why are these other,
supposedly enterprise type data sources so slow? Is there a better way
to get the attributes onto a form than looping through each record,
each field? Are there steps we can take to optimize the performance of
Spatial or SDE with MapServer?
I know there are lots of other users out there using Spatial and SDE –
I’d really appreciate hearing what has worked for you.
Finally, anticipating questions on the testing technique, I do want to
stress the use of the term “informal” to describe these tests – this
was not a formal benchmarking exercise. But the results bear out the
experiences we’ve been having over months of working with these
datasets, so while the precise times are not to be taken too seriously
I think the general results are representative.
Thanks in advance.
------------------------------
Mark Adams
General Manager, Ottawa Office
DPRA Canada
440 Laurier Ave W
Suite 200
Ottawa , ON K1R 7X6
Phone: 613.782.2326
Fax: 613.782.2228
Email: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
--
Bart van den Eijnden
OSGIS, Open Source GIS
http://www.osgis.nl
