[postgis-devel] Coordinate compression for native PostGIS geometry storage?
mark.cave-ayland at siriusit.co.uk
Tue Mar 10 08:48:07 PDT 2009
Martin Davis wrote:
> Thanks, Mark. Interesting - I hadn't realized that PG already
> compresses. I can imagine that access is expensive if decompression
> needs to be done every time!
Yes, it's actually the default although you can disable it for any given
column using ALTER TABLE foo ALTER COLUMN bar SET STORAGE <option> if
you can cope with the space trade-off (I suspect for some applications
you would see quite a substantial speed-up).
> I've done some further experimentation, and am no longer quite so
> enthusiastic that binary compression for floating-point coordinates will
> be enough of a savings to be worth. Most geometry datasets I've looked
> at offer at most about 25% redundancy. This probably isn't enough to
> bother with the extra code and performance hit.
Okay, well at least we have a record of this in archives in case the
idea is revisited later.
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
t: +44 870 608 0063
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