[OSM-talk] Distribution of OSM ids could be much more useful!
Paul Norman
penorman at mac.com
Sun Nov 25 14:36:39 UTC 2018
On 2018-11-25 5:50 AM, Victor Shcherb wrote:
> What do you think?
It would be terrible for most software that I am aware of that can
process the full planet. Current assumptions about density would be
broken, vastly inflating memory usage and slowing down processing.
The benefits aren't great as I see them. Using a z-order curve encoded
in the first 30 bits will help cache locality, but like all z-order
curves, it doesn't guarantee that two nearby places in 2d space have
nearby places on the curve. This means that an implementation still
needs to be able to search through the nodes for nearby ones.
Two other problems come to mind. The first of these is implementation.
IDs are a PostgreSQL bigserial, and to write something custom that
assigns IDs based on location would be difficult as it would need to get
MVCC right. The second is the number of bits. Some software is limited
to 53-59 bits, and other to 63 bits. We're using about 75% of 33 bits
right now.
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