As of PostGIS 2.3, the postgis extension was changed to no longer allow relocation. All function calls within the extension are now schema qualified.
While this change fixed some issues with database restore, it created the issue of if you installed PostGIS in a schema other than the one you wanted to it is not intuitive how to move it to a different schema. Luckily there is a way to do this.
For this exercise, I will install PostGIS in the default schema and then demonstrate how to move it into another schema location.
You can run these steps using psql or pgAdmin or any other PostgreSQL tool you want.
Most people have their default schema set to
so not explicitly specifying an install schema will generally install
postgis in the
CREATE EXTENSION postgis;
Now I’ll create a new schema to move it and add this schema to search_path
CREATE SCHEMA postgis; ALTER DATABASE mydb SET `search_path` = public,postgis;
If you are running PostGIS 2.3 or higher, trying to move to a different schema using the usual step:
ALTER EXTENSION postgis SET SCHEMA postgis;
will fail with error ERROR: extension “postgis” does not support SET SCHEMA.
To allow the move do these steps:
UPDATE pg_extension SET extrelocatable = TRUE WHERE extname = 'postgis'; ALTER EXTENSION postgis SET SCHEMA postgis; ALTER EXTENSION postgis UPDATE TO "2.4.1next"; ALTER EXTENSION postgis UPDATE TO "2.4.1";
Note the use of the extension version that includes
next version step is needed in order to upgrade all the schema qualified function references to
the new schema location.
next is designed to allow upgrading a postgis extension to a version it is already on.
Trying to run UPDATE TO “2.4.1” when you are already on 2.4.1 would trigger an error that you are already on that version.
The error ‘postgis.backend’ is already set comes up every so often in PostGIS mailing list. The issue arises often during or after an upgrade. I’ll go over causes for this I am aware of and how to fix.
The question goes something like this
After upgrading to Postgis 2.3 from 2.1, my server log is filled with these messages :
“WARNING ‘postgis.backend’ is already set and cannot be changed until you reconnect”
This raster question comes up quite a bit on PostGIS mailing lists and stack overflow and the best answer often involves
the often forgotten
ST_Reclass function that has existed since PostGIS 2.0.
People often resort to the much slower though more flexible
ST_MapAlgebra or dumping out
their rasters as Pixel valued polygons they then filter
with WHERE val > 90,
ST_Reclass does the same thing but orders of magnitude faster.