X-Git-Url: https://git.openstreetmap.org/nominatim.git/blobdiff_plain/388c7f706d43be1e025ac9250b5a068dff3c0a01..d9e0ef0ebfbc2860e7c0b7e7510a4014300074be:/docs/admin/Import-and-Update.md

diff --git a/docs/admin/Import-and-Update.md b/docs/admin/Import-and-Update.md
index 847aa37d..1e55e856 100644
--- a/docs/admin/Import-and-Update.md
+++ b/docs/admin/Import-and-Update.md
@@ -58,10 +58,89 @@ Nominatim can use postcodes from an external source to improve searches that inv
     cd $NOMINATIM_SOURCE_DIR/data
     wget https://www.nominatim.org/data/gb_postcode_data.sql.gz
 
+## Choosing the Data to Import
+
+In its default setup Nominatim is configured to import the full OSM data
+set for the entire planet. Such a setup requires a powerful machine with
+at least 32GB of RAM and around 800GB of SSD hard disks. Depending on your
+use case there are various ways to reduce the amount of data imported. This
+section discusses these methods. They can also be combined.
+
+### Using an extract
+
+If you only need geocoding for a smaller region, then precomputed extracts
+are a good way to reduce the database size and import time.
+[Geofabrik](https://download.geofabrik.de) offers extracts for most countries.
+They even have daily updates which can be used with the update process described
+below. There are also
+[other providers for extracts](https://wiki.openstreetmap.org/wiki/Planet.osm#Downloading).
+
+Please be aware that some extracts are not cut exactly along the country
+boundaries. As a result some parts of the boundary may be missing which means
+that cannot compute the areas for some administrative areas.
+
+### Dropping Data Required for Dynamic Updates
+
+About half of the data in Nominatim's database is not really used for serving
+the API. It is only there to allow the data to be updated from the latest
+changes from OSM. For many uses these dynamic updates are not really required.
+If you don't plan to apply updates, the dynamic part of the database can be
+safely dropped using the following command:
+
+```
+./utils/setup.php --drop
+```
+
+Note that you still need to provide for sufficient disk space for the initial
+import. So this option is particularly interesting if you plan to transfer the
+database or reuse the space later.
+
+### Reverse-only Imports
+
+If you only want to use the Nominatim database for reverse lookups or
+if you plan to use the installation only for exports to a
+[photon](http://photon.komoot.de/) database, then you can set up a database
+without search indexes. Add `--reverse-only` to your setup command above.
+
+This saves about 5% of disk space.
+
+### Filtering Imported Data
+
+Nominatim normally sets up a full search database containing administrative
+boundaries, places, streets, addresses and POI data. There are also other
+import styles available which only read selected data:
+
+* **settings/import-admin.style**
+  Only import administrative boundaries and places.
+* **settings/import-street.style**
+  Like the admin style but also adds streets.
+* **settings/import-address.style**
+  Import all data necessary to compute addresses down to house number level.
+* **settings/import-full.style**
+  Default style that also includes points of interest.
+
+The style can be changed with the configuration `CONST_Import_Style`.
+
+To give you an idea of the impact of using the different style, the table
+below gives rough estimates of the final database size after import of a
+2018 planet and after using the `--drop` option. It also shows the time
+needed for the import on a machine with 32GB RAM, 4 CPUS and SSDs. Note that
+the given sizes are just an estimate meant for comparison of style requirements.
+Your planet import is likely to be larger as the OSM data grows with time.
+
+style     | Import time  |  DB size   |  after drop
+----------|--------------|------------|------------
+admin     |    5h        |  190 GB    |   20 GB
+street    |   42h        |  400 GB    |  180 GB
+address   |   59h        |  500 GB    |  260 GB
+full      |   80h        |  590 GB    |  320 GB
+
+You can also customize the styles further. For an description of the
+style format see [the developement section](../develop/Import.md).
 
 ## Initial import of the data
 
-**Important:** first try the import with a small excerpt, for example from
+**Important:** first try the import with a small extract, for example from
 [Geofabrik](https://download.geofabrik.de).
 
 Download the data to import and load the data with the following command: