add a section about moving the database to another machine

diff --git a/docs/admin/Advanced-Installations.md b/docs/admin/Advanced-Installations.md
index 98a3b64a10572e4ae2b537f54d33656af712b36c..ff267cee28bd45f9d15fdbef4eb4ddc83a1ddaed 100644 (file)
--- a/docs/admin/Advanced-Installations.md
+++ b/docs/admin/Advanced-Installations.md
@@ -101,7 +101,7 @@ This will get diffs from the replication server, import diffs and index
 the database. The default replication server in the
 script([Geofabrik](https://download.geofabrik.de)) provides daily updates.
 
 the database. The default replication server in the
 script([Geofabrik](https://download.geofabrik.de)) provides daily updates.
 

-## Importing Nominatim to an external PostgreSQL database
+## Using an external PostgreSQL database

 
 You can install Nominatim using a database that runs on a different server when
 you have physical access to the file system on the other server. Nominatim
 
 You can install Nominatim using a database that runs on a different server when
 you have physical access to the file system on the other server. Nominatim


@@ -109,6 +109,11 @@ uses a custom normalization library that needs to be made accessible to the
 PostgreSQL server. This section explains how to set up the normalization
 library.
 
 PostgreSQL server. This section explains how to set up the normalization
 library.
 

+!!! note
+    The external module is only needed when using the legacy tokenizer.
+    If you have choosen the ICU tokenizer, then you can ignore this section
+    and follow the standard import documentation.
+

 ### Option 1: Compiling the library on the database server
 
 The most sure way to get a working library is to compile it on the database
 ### Option 1: Compiling the library on the database server
 
 The most sure way to get a working library is to compile it on the database


@@ -167,3 +172,44 @@ NOMINATIM_DATABASE_MODULE_PATH="<directory on the database server where nominati
 
 Now change the `NOMINATIM_DATABASE_DSN` to point to your remote server and continue
 to follow the [standard instructions for importing](Import.md).
 
 Now change the `NOMINATIM_DATABASE_DSN` to point to your remote server and continue
 to follow the [standard instructions for importing](Import.md).

+
+
+## Moving the database to another machine
+
+For some configurations it may be useful to run the import on one machine, then
+move the database to another machine and run the Nominatim service from there.
+For example, you might want to use a large machine to be able to run the import
+quickly but only want a smaller machine for production because there is not so
+much load. Or you might want to do the import once and then replicate the
+database to many machines.
+
+The important thing to keep in mind when transferring the Nominatim installation
+is that you need to transfer the database _and the project directory_. Both
+parts are essential for your installation.
+
+The Nominatim database can be transferred using the `pg_dump`/`pg_restore` tool.
+Make sure to use the same version of PostgreSQL and PostGIS on source and
+target machine.
+
+!!! note
+    Before creating a dump of your Nominatim database, consider running
+    `nominatim freeze` first. Your database looses the ability to receive further
+    data updates but the resulting database is only about a third of the size
+    of a full database.
+
+Next install Nominatim on the target machine by following the standard installation
+instructions. Again make sure to use the same version as the source machine.
+
+You can now copy the project directory from the source machine to the new machine.
+If necessary, edit the `.env` file to point it to the restored database.
+Finally run
+
+    nominatim refresh --website
+
+to make sure that the local installation of Nominatim will be used.
+
+If you are using the legacy tokenizer you might also have to switch to the
+PostgreSQL module that was compiled on your target machine. If you get errors
+that PostgreSQL cannot find or access `nominatim.so` then copy the installed
+version into the `module` directory of your project directory. The installed
+copy can usually be found under `/usr/local/lib/nominatim/module/nominatim.so`.