[postgis-users] MORE THOUGHTS ABOUT PERFORMANCE IN POSTGIS

[Alvaro Zabala]

We are making some aditional probes, and we would like to ask/argue some 
questions:

Ive noticed that PostGIS spatial indexes are very fast when you ask concrete 
regions. For example: when you work with a complete layer (500.000 rows) , 
and you ask 1/15 of total region, we are recovering many thousand of rows in 
1000 ms (very good times).

The problem is when we ask regions near to complete region. (3/4). Im 
speaking about the time postgis resolve the query 
(statement.executeQuery(query) with Java JDBC). It looks that if for these 
regions, the use of spatial index doesnt help.

What is the reason? The number of points of the table? The type of query? 
etc.

Regards!

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