[postgis-users] Performance question (how many years willthistake?)

[Gregory S. Williamson]

Andrea --

Because the cell_id column has an index on it the optimizer in the postgres database will probably try to use it reduce the total number of disk accesses. The "&&" operator referred to in an earlier post will have the same effect with the spatial index on the columns it refers to.

The range in this SQL ($START_ID - $END_ID) will allow for the selection of a very small number of rows at a time, compared with the total number of rows. Again, reduces disk I/O as postgres does not have to ask for as many possible rows as viable answers to the query.

The $CELL_ID reference I don't understand ... seems like it might be either a variable with the value of cell_id or a typographic error.

Greg Williamson
DBA
GlobeXplorer LLC

-----Original Message-----
From:	Andrea Aime [mailto:andrea.aime at aliceposta.it]
Sent:	Mon 5/10/2004 11:30 PM
To:	postgis-users at postgis.refractions.net
Cc:	
Subject:	Re: [postgis-users] Performance question (how many years willthistake?)
Alle 04:04, martedì 11 maggio 2004, Wood Brent ha scritto:

...

> What I have now done is add a
>     "where cell_id >= $START_ID and $CELL_ID < $END_ID"
> into the sql, and wrap it up in a script which starts at cell_id of 0 and
> increments in batches of 100 cells per iteration until it gets to the
> maximum cell_id. (note: there is a unique index on cell_id which is an
> integer attr)

Sorry, but I've never seen that sintax... what's this and why it improves the
overlay process?
"where cell_id >= $START_ID and $CELL_ID < $END_ID"

Best regards
Andrea Aime
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