Hi Adrian,
I have used long EXPRESSION list in the past, but my data are "static", so eventually I modified the map data and removed the polygons I didn't want to render. I could suggest to you to use in your map file several LAYERs or CLASSes to "spread around" long EXPRESSION lists. Those LAYERs or CLASSes would be identical but for the EXPRESSION lists. You could put a limit of let's say 10 selected features per CLASS definition. Best regards, Nick _____ From: mapserver-users-boun...@lists.osgeo.org [mailto:mapserver-users-boun...@lists.osgeo.org] On Behalf Of Adrian Popa Sent: 14 July 2009 07:15 To: mapserver-users@lists.osgeo.org Subject: [mapserver-users] Performance in regular expressions or an alternative way to select a list of features Hello everyone, Here's my problem: I'm trying to highlight segments from a line layer by using an expression in a specific class. This portion of the mapfile is dynamically generated and when it is done, it is sent to mapserver for rendering. My problem is that I have to select between 10 - 400 features at a time and I noticed when I have a lot of features there is a severe performance degradation in mapserver (takes a lot of time to render or even times out). Right now, my expression is built using regular expressions: something like: EXPRESSION /^ITEM1$|^ITEM2$|^ITEM3$|^ITEM4$/ This works ok, but as I said has a performance penalty when you reach ~400 items. My data is selected from a shapefile layer which has about 5500 items. Since I wouldn't be using the regular expressions at full capacity (I'm matching the full name), I might rewrite the expression using something like: EXPRESSION ( ([NAME]=="ITEM1") OR ([NAME]=="ITEM2") OR ([NAME]=="ITEM3") OR ([NAME]=="ITEM4") ) >From the documentation I see that: Regular expression with MapServer work similarly to string comparison, but allow more complex operation. They are slower than pure string comparisons, but might be still faster than logical expression. As with the string comparison use regular expressions, a FILTERITEM or a CLASSITEM has to defined, respectively. I would like to know if there is an efficient way of selecting a list of elements from a layer, or what are your recommendations. Also - have there been significant changes in performance for this issue from mapserver 4.10 (I am now migrating to mapserver 5.4)? Thanks, Adrian
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