Fix & optimize incorrect function declarations (#918)

* All functions that access database must be declared as `STABLE`, not `IMMUTABLE` -- because database can change at any moment, e.g. during an update
* there are a few functions that could be made `STRICT` -- passing `NULL` as a parameter will always result in a `NULL`, but for some reason that causes a significant decrease in perf.
* tagged one function as parallel safe

NOTE: somehow `ST_AsMVT()` method of tile generation is showing 70-90% slowdown with this patch. I am not sure of why this is happening. If the reason is the `IMMUTABLE` -> `STABLE` change, we may have to dig deeper into PG optimization

layers/aerodrome_label/layer.sql

@@ -38,5 +38,6 @@ SELECT
 FROM osm_aerodrome_label_point
 WHERE geometry && bbox
   AND zoom_level >= 10;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/aeroway/layer.sql

@@ -56,5 +56,6 @@ FROM (
          WHERE zoom_level >= 14
      ) AS zoom_levels
 WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/boundary/boundary.sql

@@ -206,7 +206,10 @@ SELECT CASE
                THEN replace(SUBSTRING(name, POSITION(' at ' IN name) + 4), ' ', '')
            ELSE replace(replace(name, ' ', ''), 'Extentof', '')
            END;
-$$ LANGUAGE SQL IMMUTABLE;
+$$ LANGUAGE SQL IMMUTABLE
+                -- STRICT
+                PARALLEL SAFE
+                ;
 
 
 -- etldoc: ne_110m_admin_0_boundary_lines_land  -> boundary_z0
@@ -625,5 +628,6 @@ FROM (
          WHERE geometry && bbox
            AND zoom_level >= 13
      ) AS zoom_levels;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/building/building.sql

@@ -112,6 +112,9 @@ FROM (
            AND geometry && bbox
      ) AS zoom_levels
 ORDER BY render_height ASC, ST_YMin(geometry) DESC;
-$$ LANGUAGE SQL IMMUTABLE;
+$$ LANGUAGE SQL STABLE
+                -- STRICT
+                PARALLEL SAFE
+                ;
 
 -- not handled: where a building outline covers building parts

layers/housenumber/layer.sql

@@ -18,5 +18,6 @@ SELECT
 FROM osm_housenumber_point
 WHERE zoom_level >= 14
   AND geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/landcover/landcover.sql

@@ -15,6 +15,7 @@ SELECT CASE
            %%FIELD_MAPPING: class %%
            END;
 $$ LANGUAGE SQL IMMUTABLE
+                -- STRICT
                 PARALLEL SAFE;
 
 -- etldoc: ne_110m_glaciated_areas ->  landcover_z0
@@ -185,5 +186,6 @@ FROM (
          WHERE zoom_level >= 14
            AND geometry && bbox
      ) AS zoom_levels;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/landuse/landuse.sql

@@ -214,5 +214,6 @@ FROM (
          WHERE zoom_level >= 14
      ) AS zoom_levels
 WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/mountain_peak/layer.sql

@@ -57,5 +57,6 @@ WHERE zoom_level >= 7
   AND (rank <= 5 OR zoom_level >= 14)
 ORDER BY "rank" ASC;
 
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
                 PARALLEL SAFE;
+-- TODO: Check if the above can be made STRICT -- i.e. if pixel_width could be NULL

layers/park/layer.sql

@@ -336,5 +336,6 @@ FROM (
                     AND geometry_point && bbox
               ) AS park_point
      ) AS park_all;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
                 PARALLEL SAFE;
+-- TODO: Check if the above can be made STRICT -- i.e. if pixel_width could be NULL

layers/place/city.sql

@@ -74,5 +74,6 @@ FROM (
             OR (zoom_level BETWEEN 11 AND 12 AND (gridrank <= 14 OR "rank" IS NOT NULL))
             OR (zoom_level >= 13)
      ) AS city_all;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/place/layer.sql

@@ -142,5 +142,6 @@ FROM (
          FROM layer_city(bbox, zoom_level, pixel_width)
          ORDER BY "rank" ASC
      ) AS place_all
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
                 PARALLEL SAFE;
+-- TODO: Check if the above can be made STRICT -- i.e. if pixel_width could be NULL

layers/poi/layer.sql

@@ -94,5 +94,6 @@ FROM (
            AND zoom_level >= 14
      ) AS poi_union
 ORDER BY "rank"
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
                 PARALLEL SAFE;
+-- TODO: Check if the above can be made STRICT -- i.e. if pixel_width could be NULL

layers/transportation/layer.sql

@@ -698,5 +698,6 @@ FROM (
      ) AS zoom_levels
 WHERE geometry && bbox
 ORDER BY z_order ASC;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/transportation_name/layer.sql

@@ -147,5 +147,6 @@ FROM (
      ) AS zoom_levels
 WHERE geometry && bbox
 ORDER BY z_order ASC;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/water/water.sql

@@ -385,5 +385,6 @@ FROM (
          WHERE zoom_level >= 14
      ) AS zoom_levels
 WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/water_name/layer.sql

@@ -74,5 +74,6 @@ WHERE geometry && bbox
         OR (zoom_level >= "rank" AND "rank" IS NOT NULL)
         OR (zoom_level >= 8)
     );
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;

layers/waterway/waterway.sql

@@ -220,5 +220,6 @@ FROM (
          WHERE zoom_level >= 14
      ) AS zoom_levels
 WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE
+$$ LANGUAGE SQL STABLE
+                -- STRICT
                 PARALLEL SAFE;