[postgis-users] Buffer Performance

[Alexander Pucher]

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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