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<DIV><SPAN class=204313117-12032004><FONT face=Arial color=#0000ff size=2>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.</FONT></SPAN></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV align=center><FONT face=Arial size=2>Martin Davis, Senior Technical
Architect<BR><STRONG><FONT color=#0000ff>Vivid Solutions
Inc.</FONT></STRONG><BR><EM>Suite #1A-2328 Government Street Victoria, B.C. V8T
5G5<BR>Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046</EM></FONT></DIV>
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<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left><FONT
face=Tahoma size=2>-----Original Message-----<BR><B>From:</B> Alexander Pucher
[mailto:pucher@atlas.gis.univie.ac.at] <BR><B>Sent:</B> Friday, March 12, 2004
3:39 AM<BR><B>To:</B> PostGIS Users Discussion<BR><B>Subject:</B>
[postgis-users] Buffer Performance<BR><BR></FONT></DIV><FONT
face="Helvetica, Arial, sans-serif">Hi,<BR><BR>did some buffer performance
testing with a table that holds about 2100 multilinestrings (river network of
europe).<BR><BR>'select buffer(the_geom,5) from river;'<BR><BR>takes about 7
seconds to execute, whereas<BR></FONT><FONT
face="Helvetica, Arial, sans-serif"><BR>'select buffer(the_geom,15000) from
river' <BR><BR>takes a couple of minutes...<BR><BR>The 'river' table is not
indexed, if this might be of importance ?!?<BR><BR>'explain select....'
<BR><BR>shows similar output for both queries:<BR><BR>QUERY
PLAN<BR>-----------------------------------------------------------<BR> Seq
Scan on river (cost=0.00..139.51 rows=2051 width=32)<BR>(1
row)<BR><BR><BR>What's the reason for the difference in execution time,
depending on the buffer size?<BR>Is there a way to speed up </FONT><FONT
face="Helvetica, Arial, sans-serif">execution time of </FONT><FONT
face="Helvetica, Arial, sans-serif">such queries??<BR><BR>Best
regards,<BR>alex.<BR></FONT><FONT
face="Helvetica, Arial, sans-serif"><BR></BLOCKQUOTE></FONT></BODY></HTML>