On 4/28/2012 9:44 AM, Puneet Kishor wrote:
On Apr 28, 2012, at 8:20 AM, Stephen
Woodbridge<[email protected]> wrote:
On 4/28/2012 8:44 AM, Matt McClelland wrote:
Hi All
I have a set of contours in a SHP file If I point my map file to
the SHP file I can generate a WMS image in under 1 second Shp
file is just shy of 200MB
I then use shp2pgsql to load the same dataset into the DB I added
an index for the_geom And am requesting the data in the mapfile
using the same EPSG
The map draws correclty but is now taking about 30secs when using
the DB.
Any ideas on how to make it faster.
Simplify the data for the that zoom level.
If you are all the way zoomed out and drawing all the data, then
the shapefile will be fastest. An index does not help if you are
drawing all the data as you need to do a full table scan anyway to
get all the records. It is simply faster to read 200MB from disk
than from the database because the database has to fetch the same
data and may have to jump through some hoops to get it out of
extended storage, then it has to encode the data and send it over
the connection and the client has to decode the data.
Do you really need all the resolution of the data at this scale? If
not create another column and simplify the geometry into that
column and set up your mapfile to query the simplified data at this
zoom and to query the detailed data as you zoom in.
All of the above is great advice. Additionally, implement a tilecache
server; why redraw an image if it has already been drawn.
That said, while a db is going to be slower than the file system in
many cases, there are many reasons why your db is performing so
slowly. Thirty times slow is too much, and 30s for a query, no matter
what query, is wrong. Benchmark your entire stack to find
bottlenecks... Is the query itself taking that long? Is something
else going wrong? Is the exact query that MapServer is performing
actually using your indexes?
In pgAdmin or from the psql commandline, how long does it take to do:
select * from yourtable;
Do you have the exact query that mapserver is making? You can get it by
adding to the MAP object
DEBUG 10
CONFIG MS_ERRORFILE "stderr"
then looking in the apache error_log.
-Steve
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