forked from hans/Nominatim
52 lines
2.2 KiB
Markdown
52 lines
2.2 KiB
Markdown
This chapter describes the various operations the Nominatim database administrator
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may use to clean and maintain the database. None of these operations is mandatory
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but they may help improve the performance and accuracy of results.
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## Updating postcodes
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Command: `nominatim refresh --postcodes`
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Postcode centroids (aka 'calculated postcodes') are generated by looking at all
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postcodes of a country, grouping them and calculating the geometric centroid.
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There is currently no logic to deal with extreme outliers (typos or other
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mistakes in OSM data). There is also no check if a postcodes adheres to a
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country's format, e.g. if Swiss postcodes are 4 digits.
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When running regular updates, postcodes results can be improved by running
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this command on a regular basis. Note that only the postcode table and the
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postcode search terms are updated. The postcode that is assigned to each place
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is only updated when the place is updated.
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The command takes around 70min to run on the planet and needs ca. 40GB of
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temporary disk space.
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## Updating word counts
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Command: `nominatim refresh --word-counts`
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Nominatim keeps frequency statistics about all search terms it indexes. These
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statistics are currently used to optimise queries to the database. Thus better
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statistics mean better performance. Word counts are created once after import
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and are usually sufficient even when running regular updates. You might want
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to rerun the statistics computation when adding larger amounts of new data,
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for example, when adding an additional country via `nominatim add-data`.
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## Removing large deleted objects
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Nominatim refuses to delete very large areas because often these deletions are
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accidental and are reverted within hours. Instead the deletions are logged in
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the `import_polygon_delete` table and left to the administrator to clean up.
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There is currently no command to do that. You can use the following SQL
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query to force a deletion on all objects that have been deleted more than
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a certain timespan ago (here: 1 month):
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```sql
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SELECT place_force_delete(p.place_id) FROM import_polygon_delete d, placex p
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WHERE p.osm_type = d.osm_type and p.osm_id = d.osm_id
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and age(p.indexed_date) > '1 month'::interval
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```
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