[postgis-users] Rasters -- disk paging

[Gregory S. Williamson]

Without addressing any of the worthwhile questions below, let me add a foolish question --

Is it possible to adjust the amount of data transferred in one chunk in postgres ?

I've used Informix systems with BLOBs in which we could change the page size from 2k (standard for most Informix versions) -- in our case we knew that 95% of our TIFFs would fit in a 20k blob, so we defined the BLOBs for that application to use that size -- made it very efficient in that one read / write operation involved only one disk operation, rather than multiple 2k transfers. (of course that other 5% of images waste some disk space and took 2 transfers...). With Informix "raw" storage we found this to be at least as fast as standard file system storage of TIFFs.

Or is this irrelevant given postgres' underlying data storage (e.g. TOAST etc.) ?

Greg W.

-----Original Message-----
From:	postgis-users-bounces at postgis.refractions.net on behalf of Paul Ramsey
Sent:	Thu 9/29/2005 8:39 AM
To:	PostGIS Users Discussion
Cc:	
Subject:	[postgis-users] Rasters
OK, raster people.  My problem is that I cannot envision the use  
cases for raster in the database, so, make it easy for me! :)

- What is the atomic unit of storage for rasters in the database?  Is  
it complete scenes?  Something else?
- What is some SQL I would apply against my raster tables?  Make up  
some descriptive function names and show me some example SQL and tell  
me what it does.
- How do vector data and raster data interact?  Note the atomicity  
question above.

P.
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