[OSM-dev] history & disk space

Dirk-Lüder Kreie osm-list at deelkar.net
Thu Sep 27 12:34:17 BST 2007

Hash: SHA1

Steve Coast schrieb:
> When I last looked when you added a object the server
> a) inserts the data in to the current nodes table
> b) inserts the same data in to a node history table
> When you update it
> a) updates the data in the current nodes table
> b) inserts the same data in to a node history table
> So we use at least twice the storage space. We could change this so  
> that history is only added on an update and not by default on  
> creation. It creates overhead in that when you look up the history of  
> an object it needs to check both the history and current table (which  
> I'm guessing is a rare API call), but saves some large number of Gb  
> in space.
> Thoughts?

I think we only waste double the space if the objects never get updated.
else it's 1.5 times to 1.000...01 times, depending on the amount of
updates and history data kept.

however I think that instead of inserting the data to both the history
and current table you should insert only "old" data to the history, and
fetch the current state from the current table like you proposed.

Especially since most of the bulk imports that are going on are
remaining unchanged or even remaining unchecked for quite some time.

- --

Dirk-Lüder "Deelkar" Kreie
Bremen - 53.0952°N 8.8652°E

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