When processing updates, osm2pgsql will handle deleted objects by simply deleting them from the database. A changed object is handled as if it was deleted and a new object created after that. But users often want to do some extra processing when an object is deleted or changed.
Currently this can be handled by adding database triggers that do something else instead of the delete. But that is somewhat cumbersome and, for changed objects, we have to fit the “delete” and the “insert” together again to find out that we had a “change” originally, something we knew at the start of the processing chain, but that information is lost once we are inside the database.
We might need some extra callbacks into the Lua code for this and/or change the DELETE/COPY we are doing now into some kind of “UPSERT”.
When processing updates, osm2pgsql will handle deleted objects by simply deleting them from the database. A changed object is handled as if it was deleted and a new object created after that. But users often want to do some extra processing when an object is deleted or changed.
Currently this can be handled by adding database triggers that do something else instead of the delete. But that is somewhat cumbersome and, for changed objects, we have to fit the “delete” and the “insert” together again to find out that we had a “change” originally, something we knew at the start of the processing chain, but that information is lost once we are inside the database.
We might need some extra callbacks into the Lua code for this and/or change the DELETE/COPY we are doing now into some kind of “UPSERT”.