[postgis-users] Buffer Performance

[Martin Davis]

The performance difference is probably due to the difference in the
buffer widths.  In general, larger buffer widths require longer to
compute than smaller ones.  This is due to the greater interaction
(intersections) between the offset curves computed to build the buffer
curve.
 
 
Martin Davis, Senior Technical Architect
Vivid Solutions Inc.
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046

	-----Original Message-----
	From: Alexander Pucher [mailto:pucher at atlas.gis.univie.ac.at] 
	Sent: Friday, March 12, 2004 3:39 AM
	To: PostGIS Users Discussion
	Subject: [postgis-users] Buffer Performance
	
	
	Hi,
	
	did some buffer performance testing with a table that holds
about 2100 multilinestrings (river network of europe).
	
	'select buffer(the_geom,5) from river;'
	
	takes about 7 seconds to execute, whereas
	
	'select buffer(the_geom,15000) from river' 
	
	takes a couple of minutes...
	
	The 'river' table is not indexed, if this might be of importance
?!?
	
	'explain select....' 
	
	shows similar output for both queries:
	
	QUERY PLAN
	-----------------------------------------------------------
	 Seq Scan on river  (cost=0.00..139.51 rows=2051 width=32)
	(1 row)
	
	
	What's the reason for the difference in execution time,
depending on the buffer size?
	Is there a way to speed up execution time of such queries??
	
	Best regards,
	alex.
	
	

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