Yeah, this sounds like it will run for a very very long time. A couple
of thoughts that have more to do with managing the process:
1) make sure you run an is_valid() check on both tables and remove/fix
any geometries that are not valid. It is a pain when you hit one of
these and it nukes your transaction or crashes the server and you have
to start over.
2) you might want to break this into multiple queries based on some
subset of the record in the smaller table. Like do 1-10000, 10001-20000,
etc. This would allow you to get the results of each commited so a
restart would be less painful, also this would allow you to get some
timing statistics to better predict how long the remainder of the rows
will take.
-Steve
niels hoffmann wrote:
Hi,
I am fairly new to Postgis so I like some feedback whether I am going
through the right moves.
I am trying to create a new table with the intersected results from two
input polygon tables.
Both tables are in NZMG (2193) the first table has 100000+ records, the
second table has 400000+ records.
The query I am using is:
Create table ablc_pol with OIDS as
SELECT intersection(a.geom, l.geom) as intersect_geom, a.*,
l."CLASS",l."NAME", l."REPLID"
from first_table a, second_table l
Where a.geom && l.geom
AND intersects(a.geom, l.geom);
Currently this query is taking >200 hours before I cancelled it because
I wasn't sure it would ever end. However, running it on a small subset
showed satisfactory results...
I am using version 1.2 on Windows.
Does it matter which table I put first in the query or would the
optimizer take care of that?
Cheers,
Niels
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